Một đoạn gen có tổng chiều dài là 7956,trong đó T chiếm 30%.Khi đột biến gen bị mất 3 cặp G-X. a) Xác định số nu từng loại trước và sau khi đột biến b) Tính chiều dài của gen trước và sau khi đột biến c) Tính số liên kết hiđro của gen trước và sau khi đột biến

III. Choose the best answer: 1. Nam …………………………his homework when I came in. A. do B.was doing C. is doing D. does 2. Nga has worked in this company ……………………. 6 years. A. since B.in C.for D. at 3. When I got to the hospital , she _____ in the waiting room. A. sat B. was sitting C. had sat D. is sitting. 4. Can you tell me how ______ this washing machine ? A. to operate B. I could operate C. operating D. could I operate 5. John ___ at the moment, so he can’t answer the telephone. A. works B. is working C. has worked D. will work 6. I ___ my key. Can you help me look for it? A. lose B. lost C. had lost D. have lost 7. Last week, Dick ___ his right leg. A. falls and breaks B. fell and breaks C. fell and broke D. falls and broke 8. The moon ___ round the earth. A. goes B. is going C. will go D. went 9. Last night, Tina ___ in bed when suddenly she heard a scream. A. read B. was reading C. has read D. had read 10.Ann lives in London. She ___ there for 10 years. A. has been living B. is living C. was living D. had been living 11. How many language ___ John speak? A. do B. does C. did D. will 12. Look! Someone ___ to open your car door. A. is trying B. has been trying C. are trying D. were trying 13. Since 1981, scientists in the world ___ a lot of things to fight AIDS. A. had done B. has done C. have done D. did 14. This room is dirty. Someone ___ here. A. smoked B. has smoked C. had been smoking D. has been smoking 15. Mike ___ one hour ago. A. phoned B. was phoning C. had phoned D. has phoned 16. I was so embarrassed, I was sure that someone ___ at me. A. were looking B. was looking C. has been looking D. is looking 17. Paulo has learned English ___ five years. A. since B. from C. to D. for 18. Oh! I’ve cut my finger. It ___ . A. bleeds B. is bleeding C. had bleed D. was bleeding 19. When you ___ to England this summer, please visit me. A. will come B. came C. come D. are coming 20. Families in the Western world ___ very much in the last 100 years. A. changed B. has changed C. had changed D. have changed 21. It ___ five years since he ___ to study English. A. was/ begin B. is/ has begun C. will be/ begins D. is/ begun 22. Monica ___ with her sister at the moment until she find a flat. A. stays B. is staying C. will stay D. is going to stay 23. Laura says she is 17 but I ___ her. A. don’t believe B. didn’t believe C. won’t believe D. wouldn’t believe 24. When he worked here, Simon ___ mistake. A. always made B. made always C. was always making D. was making always 25. I___ work when I saw the accident. A. had driven B. am driving C. drove D. was driving 26. Since he bought a car, he ___ to work everyday. A. drives B. is driving C. has driven D. has been driving 27. Her husband ___ unemployed since they ___ the countryside. A. was/ moved B. was/ have moved C. has been/ moved D. has been/ have moved 28. We ___ our evening meal at half past seven yesterday and then we watched a film on TV. A. was having B. were having C. had D. had had 29. Tim ___ in three movies already. I think he ….. a star someday. A. had appeared/ is going tobe B. has appeared / will be C. was appearing/ is going tobe D. is appearing/ will be 30. Please don’t make so much noise. My son ___. A. sleeps B. is sleeping C. slept D. has been sleeping 31. When the storm ___ this area tomorrow, it will bring with it great destruction force. A. is reaching B. will reach C. reaches D. is going to reach 32. While my mother ____ dinner the phone rang. A. cooked B. had cooked C. has cooked D. was cooking 33. There is nobody in the room but there is a smell of cigarettes. Somebody ___ . A. has smoked C. has been smoking B. have been smoking D. had been smoking 34. His answers to our question ___ everything so far. A. changes B. change C. has changed D. have changed 35. I’ll handle over all my files to my assistant before I ___ . A. am leaving B. leave C. will leave D. shall leave 36. I saw Maggie at the party. She ___ a very beautiful dress. A. wears B. wore C. was wearing D. has wore 37. He ___ in the U.S.A at the present. A. studies B. has studied C. is studying D. will study 38. The students ___ busily when Miss Brown went to get a book. A. had written B. were writing C. has written D. was writing 39. Angelina Jolie is a famous actress. She ___ in several films. A. appears B. is appearing C. appeared D. has appeared 40. I’ll see him when he ___ next week. A. will arrive B. arrives C. has arrived D. would arrive 41. When the old school friends met, a lot of memories ___ back. A. had brought B. were brought C. brought D. had been brought 42. She ___ away when he came in. A. went B. was going C. had gone D. has gone 43. I ___ stamps since I was 10 years old. A. collected B. had collected C. have collected D. was collecting 44. They ___ TV when the light went out. A. were watching B. had been watching C. had watched D. watched 45. Spring ___ winter. A. follows B. is following C. will follow D. followed 46. What time ___ the train leave yesterday? A. did B. will C. shall D. would 47. ___ you ___ the Titanic yet? A. Do/ see B. Are/ seeing C. Have/ seen D. Will/ see 48. He ___ for Chelsea this season. A. played B. is playing C. would play D. has played 49. Jane’s eyes are red. She ___ . A. cried B. has cried C. has been crying D. had cried 50. Michael ___ a work with Lisa this morning. A. has B. had C. has had D. had had 51. I________ "Chicken soup for the soul" but I haven’t finished it yet. a. read b. am reading c. have been reading d. was reading 52. Alan took a photograph of Sandra while she________ a. didn't look b. wasn't looking c. hasn't looked d.. hadn't looked 53. I ________ my key. Can you help me look for it? a. lose b. lost c. had lost d. have lost 54. Last night Tine________ in bed when suddenly she heard a scream. a. read b. was reading c. had read d. had read 55. We________ a part next week. Would you like to come? a. have b. will have c. are having d. will have had 56. The Red River________ very fast today-much faster than yesterday. a. flows b. is flowing c. will flow d. is going to flow 57. While mother________ dinner the phone rang. a. cooked b. had cooked c. has cooked d. was cooking 58. Fish________ on earth for ages and ages. a. existed b. are existing c. exist d. have existed 59. The phone________ constantly since Jack won the first prize this morning. a. has been ringing b. rang c. had rung d. had been ringing 60. The earth________ on the sun for its heat and light. a. is depend b. depending c. has depend d. depends 61. I don't feel good. I ________ home from work tomorrow. a. am staying b. stay c. will have stayed d. stayed 62. In the last two decades, space exploration___great contributions to weather forecasting. a. is making b. has made c. made d. makes 63. On July 20, 1969, Neil Armstrong ___down onto the moon, the first person ever set foot on another planet. a. was stepping b. stepped c. has stepped d. was step 64. When boarding the plane, many passengers were annoyed because they ________ waiting in the airport for three ad a half hours. a. are b. were c. have been d. had been 65. By the end of this year, Tom ________English for three years. a. will be studying b. has studied c. will have studied d. has been studying 66. They ________ this course by next June. a. have finished b. will finish c. are going to finish d. will have finished 67. She will go abroad as soon as she________ this English course. a. has completed b. will complete c. will have completed d. completed 68. I / have/ wonderful time/ Da Lat/ moment A. I was having a wonderful time in Da Lat in the moment. B. I am having a wonderful time in Da Lat at the moment. C. I had a wonderful time in Da Lat at the moment. D. I am having a wonderful time at Da Lat in the moment. 69. I / already / visit / Xuan Huong Lake / Prenn Waterfall/ places of interest. A. I have already visit Xuan Huong Lake, Prenn Waterfall and some places of interest. B. I have already visited Xuan Huong Lake, Prenn Waterfall and some places of interest. C. I was already visiting Xuan Huong Lake, Prenn Waterfall and some places of interest. D. I am already visiting Xuan Huong Lake, Prenn Waterfall and some places of interest. 70. Last night/ I / visit/ Da Lat market / buy / lot/ souvernirs . A. Last night I visit Da Lat market and buy lots of souvernirs. B. Last night I was visiting Da Lat market and buying lots of souvenirs. C. Last night I visited Da Lat market and bought a lot of souvenirs. D. Last night I have visited Da Lat market and bought a lot of souvenirs. III. Choose the best answer: 1. Nam …………………………his homework when I came in. A. do B.was doing C. is doing D. does 2. Nga has worked in this company ……………………. 6 years. A. since B.in C.for D. at 3. When I got to the hospital , she _____ in the waiting room. A. sat B. was sitting C. had sat D. is sitting. 4. Can you tell me how ______ this washing machine ? A. to operate B. I could operate C. operating D. could I operate 5. John ___ at the moment, so he can’t answer the telephone. A. works B. is working C. has worked D. will work 6. I ___ my key. Can you help me look for it? A. lose B. lost C. had lost D. have lost 7. Last week, Dick ___ his right leg. A. falls and breaks B. fell and breaks C. fell and broke D. falls and broke 8. The moon ___ round the earth. A. goes B. is going C. will go D. went 9. Last night, Tina ___ in bed when suddenly she heard a scream. A. read B. was reading C. has read D. had read 10.Ann lives in London. She ___ there for 10 years. A. has been living B. is living C. was living D. had been living 11. How many language ___ John speak? A. do B. does C. did D. will 12. Look! Someone ___ to open your car door. A. is trying B. has been trying C. are trying D. were trying 13. Since 1981, scientists in the world ___ a lot of things to fight AIDS. A. had done B. has done C. have done D. did 14. This room is dirty. Someone ___ here. A. smoked B. has smoked C. had been smoking D. has been smoking 15. Mike ___ one hour ago. A. phoned B. was phoning C. had phoned D. has phoned 16. I was so embarrassed, I was sure that someone ___ at me. A. were looking B. was looking C. has been looking D. is looking 17. Paulo has learned English ___ five years. A. since B. from C. to D. for 18. Oh! I’ve cut my finger. It ___ . A. bleeds B. is bleeding C. had bleed D. was bleeding 19. When you ___ to England this summer, please visit me. A. will come B. came C. come D. are coming 20. Families in the Western world ___ very much in the last 100 years. A. changed B. has changed C. had changed D. have changed 21. It ___ five years since he ___ to study English. A. was/ begin B. is/ has begun C. will be/ begins D. is/ begun 22. Monica ___ with her sister at the moment until she find a flat. A. stays B. is staying C. will stay D. is going to stay 23. Laura says she is 17 but I ___ her. A. don’t believe B. didn’t believe C. won’t believe D. wouldn’t believe 24. When he worked here, Simon ___ mistake. A. always made B. made always C. was always making D. was making always 25. I___ work when I saw the accident. A. had driven B. am driving C. drove D. was driving 26. Since he bought a car, he ___ to work everyday. A. drives B. is driving C. has driven D. has been driving 27. Her husband ___ unemployed since they ___ the countryside. A. was/ moved B. was/ have moved C. has been/ moved D. has been/ have moved 28. We ___ our evening meal at half past seven yesterday and then we watched a film on TV. A. was having B. were having C. had D. had had 29. Tim ___ in three movies already. I think he ….. a star someday. A. had appeared/ is going tobe B. has appeared / will be C. was appearing/ is going tobe D. is appearing/ will be 30. Please don’t make so much noise. My son ___. A. sleeps B. is sleeping C. slept D. has been sleeping 31. When the storm ___ this area tomorrow, it will bring with it great destruction force. A. is reaching B. will reach C. reaches D. is going to reach 32. While my mother ____ dinner the phone rang. A. cooked B. had cooked C. has cooked D. was cooking 33. There is nobody in the room but there is a smell of cigarettes. Somebody ___ . A. has smoked C. has been smoking B. have been smoking D. had been smoking 34. His answers to our question ___ everything so far. A. changes B. change C. has changed D. have changed 35. I’ll handle over all my files to my assistant before I ___ . A. am leaving B. leave C. will leave D. shall leave 36. I saw Maggie at the party. She ___ a very beautiful dress. A. wears B. wore C. was wearing D. has wore 37. He ___ in the U.S.A at the present. A. studies B. has studied C. is studying D. will study 38. The students ___ busily when Miss Brown went to get a book. A. had written B. were writing C. has written D. was writing 39. Angelina Jolie is a famous actress. She ___ in several films. A. appears B. is appearing C. appeared D. has appeared 40. I’ll see him when he ___ next week. A. will arrive B. arrives C. has arrived D. would arrive 41. When the old school friends met, a lot of memories ___ back. A. had brought B. were brought C. brought D. had been brought 42. She ___ away when he came in. A. went B. was going C. had gone D. has gone 43. I ___ stamps since I was 10 years old. A. collected B. had collected C. have collected D. was collecting 44. They ___ TV when the light went out. A. were watching B. had been watching C. had watched D. watched 45. Spring ___ winter. A. follows B. is following C. will follow D. followed 46. What time ___ the train leave yesterday? A. did B. will C. shall D. would 47. ___ you ___ the Titanic yet? A. Do/ see B. Are/ seeing C. Have/ seen D. Will/ see 48. He ___ for Chelsea this season. A. played B. is playing C. would play D. has played 49. Jane’s eyes are red. She ___ . A. cried B. has cried C. has been crying D. had cried 50. Michael ___ a work with Lisa this morning. A. has B. had C. has had D. had had 51. I________ "Chicken soup for the soul" but I haven’t finished it yet. a. read b. am reading c. have been reading d. was reading 52. Alan took a photograph of Sandra while she________ a. didn't look b. wasn't looking c. hasn't looked d.. hadn't looked 53. I ________ my key. Can you help me look for it? a. lose b. lost c. had lost d. have lost 54. Last night Tine________ in bed when suddenly she heard a scream. a. read b. was reading c. had read d. had read 55. We________ a part next week. Would you like to come? a. have b. will have c. are having d. will have had 56. The Red River________ very fast today-much faster than yesterday. a. flows b. is flowing c. will flow d. is going to flow 57. While mother________ dinner the phone rang. a. cooked b. had cooked c. has cooked d. was cooking 58. Fish________ on earth for ages and ages. a. existed b. are existing c. exist d. have existed 59. The phone________ constantly since Jack won the first prize this morning. a. has been ringing b. rang c. had rung d. had been ringing 60. The earth________ on the sun for its heat and light. a. is depend b. depending c. has depend d. depends 61. I don't feel good. I ________ home from work tomorrow. a. am staying b. stay c. will have stayed d. stayed 62. In the last two decades, space exploration___great contributions to weather forecasting. a. is making b. has made c. made d. makes 63. On July 20, 1969, Neil Armstrong ___down onto the moon, the first person ever set foot on another planet. a. was stepping b. stepped c. has stepped d. was step 64. When boarding the plane, many passengers were annoyed because they ________ waiting in the airport for three ad a half hours. a. are b. were c. have been d. had been 65. By the end of this year, Tom ________English for three years. a. will be studying b. has studied c. will have studied d. has been studying 66. They ________ this course by next June. a. have finished b. will finish c. are going to finish d. will have finished 67. She will go abroad as soon as she________ this English course. a. has completed b. will complete c. will have completed d. completed 68. I / have/ wonderful time/ Da Lat/ moment A. I was having a wonderful time in Da Lat in the moment. B. I am having a wonderful time in Da Lat at the moment. C. I had a wonderful time in Da Lat at the moment. D. I am having a wonderful time at Da Lat in the moment. 69. I / already / visit / Xuan Huong Lake / Prenn Waterfall/ places of interest. A. I have already visit Xuan Huong Lake, Prenn Waterfall and some places of interest. B. I have already visited Xuan Huong Lake, Prenn Waterfall and some places of interest. C. I was already visiting Xuan Huong Lake, Prenn Waterfall and some places of interest. D. I am already visiting Xuan Huong Lake, Prenn Waterfall and some places of interest. 70. Last night/ I / visit/ Da Lat market / buy / lot/ souvernirs . A. Last night I visit Da Lat market and buy lots of souvernirs. B. Last night I was visiting Da Lat market and buying lots of souvenirs. C. Last night I visited Da Lat market and bought a lot of souvenirs. D. Last night I have visited Da Lat market and bought a lot of souvenirs. III. Choose the best answer: 1. Nam …………………………his homework when I came in. A. do B.was doing C. is doing D. does 2. Nga has worked in this company ……………………. 6 years. A. since B.in C.for D. at 3. When I got to the hospital , she _____ in the waiting room. A. sat B. was sitting C. had sat D. is sitting. 4. Can you tell me how ______ this washing machine ? A. to operate B. I could operate C. operating D. could I operate 5. John ___ at the moment, so he can’t answer the telephone. A. works B. is working C. has worked D. will work 6. I ___ my key. Can you help me look for it? A. lose B. lost C. had lost D. have lost 7. Last week, Dick ___ his right leg. A. falls and breaks B. fell and breaks C. fell and broke D. falls and broke 8. The moon ___ round the earth. A. goes B. is going C. will go D. went 9. Last night, Tina ___ in bed when suddenly she heard a scream. A. read B. was reading C. has read D. had read 10.Ann lives in London. She ___ there for 10 years. A. has been living B. is living C. was living D. had been living 11. How many language ___ John speak? A. do B. does C. did D. will 12. Look! Someone ___ to open your car door. A. is trying B. has been trying C. are trying D. were trying 13. Since 1981, scientists in the world ___ a lot of things to fight AIDS. A. had done B. has done C. have done D. did 14. This room is dirty. Someone ___ here. A. smoked B. has smoked C. had been smoking D. has been smoking 15. Mike ___ one hour ago. A. phoned B. was phoning C. had phoned D. has phoned 16. I was so embarrassed, I was sure that someone ___ at me. A. were looking B. was looking C. has been looking D. is looking 17. Paulo has learned English ___ five years. A. since B. from C. to D. for 18. Oh! I’ve cut my finger. It ___ . A. bleeds B. is bleeding C. had bleed D. was bleeding 19. When you ___ to England this summer, please visit me. A. will come B. came C. come D. are coming 20. Families in the Western world ___ very much in the last 100 years. A. changed B. has changed C. had changed D. have changed 21. It ___ five years since he ___ to study English. A. was/ begin B. is/ has begun C. will be/ begins D. is/ begun 22. Monica ___ with her sister at the moment until she find a flat. A. stays B. is staying C. will stay D. is going to stay 23. Laura says she is 17 but I ___ her. A. don’t believe B. didn’t believe C. won’t believe D. wouldn’t believe 24. When he worked here, Simon ___ mistake. A. always made B. made always C. was always making D. was making always 25. I___ work when I saw the accident. A. had driven B. am driving C. drove D. was driving 26. Since he bought a car, he ___ to work everyday. A. drives B. is driving C. has driven D. has been driving 27. Her husband ___ unemployed since they ___ the countryside. A. was/ moved B. was/ have moved C. has been/ moved D. has been/ have moved 28. We ___ our evening meal at half past seven yesterday and then we watched a film on TV. A. was having B. were having C. had D. had had 29. Tim ___ in three movies already. I think he ….. a star someday. A. had appeared/ is going tobe B. has appeared / will be C. was appearing/ is going tobe D. is appearing/ will be 30. Please don’t make so much noise. My son ___. A. sleeps B. is sleeping C. slept D. has been sleeping 31. When the storm ___ this area tomorrow, it will bring with it great destruction force. A. is reaching B. will reach C. reaches D. is going to reach 32. While my mother ____ dinner the phone rang. A. cooked B. had cooked C. has cooked D. was cooking 33. There is nobody in the room but there is a smell of cigarettes. Somebody ___ . A. has smoked C. has been smoking B. have been smoking D. had been smoking 34. His answers to our question ___ everything so far. A. changes B. change C. has changed D. have changed 35. I’ll handle over all my files to my assistant before I ___ . A. am leaving B. leave C. will leave D. shall leave 36. I saw Maggie at the party. She ___ a very beautiful dress. A. wears B. wore C. was wearing D. has wore 37. He ___ in the U.S.A at the present. A. studies B. has studied C. is studying D. will study 38. The students ___ busily when Miss Brown went to get a book. A. had written B. were writing C. has written D. was writing 39. Angelina Jolie is a famous actress. She ___ in several films. A. appears B. is appearing C. appeared D. has appeared 40. I’ll see him when he ___ next week. A. will arrive B. arrives C. has arrived D. would arrive 41. When the old school friends met, a lot of memories ___ back. A. had brought B. were brought C. brought D. had been brought 42. She ___ away when he came in. A. went B. was going C. had gone D. has gone 43. I ___ stamps since I was 10 years old. A. collected B. had collected C. have collected D. was collecting 44. They ___ TV when the light went out. A. were watching B. had been watching C. had watched D. watched 45. Spring ___ winter. A. follows B. is following C. will follow D. followed 46. What time ___ the train leave yesterday? A. did B. will C. shall D. would 47. ___ you ___ the Titanic yet? A. Do/ see B. Are/ seeing C. Have/ seen D. Will/ see 48. He ___ for Chelsea this season. A. played B. is playing C. would play D. has played 49. Jane’s eyes are red. She ___ . A. cried B. has cried C. has been crying D. had cried 50. Michael ___ a work with Lisa this morning. A. has B. had C. has had D. had had 51. I________ "Chicken soup for the soul" but I haven’t finished it yet. a. read b. am reading c. have been reading d. was reading 52. Alan took a photograph of Sandra while she________ a. didn't look b. wasn't looking c. hasn't looked d.. hadn't looked 53. I ________ my key. Can you help me look for it? a. lose b. lost c. had lost d. have lost 54. Last night Tine________ in bed when suddenly she heard a scream. a. read b. was reading c. had read d. had read 55. We________ a part next week. Would you like to come? a. have b. will have c. are having d. will have had 56. The Red River________ very fast today-much faster than yesterday. a. flows b. is flowing c. will flow d. is going to flow 57. While mother________ dinner the phone rang. a. cooked b. had cooked c. has cooked d. was cooking 58. Fish________ on earth for ages and ages. a. existed b. are existing c. exist d. have existed 59. The phone________ constantly since Jack won the first prize this morning. a. has been ringing b. rang c. had rung d. had been ringing 60. The earth________ on the sun for its heat and light. a. is depend b. depending c. has depend d. depends 61. I don't feel good. I ________ home from work tomorrow. a. am staying b. stay c. will have stayed d. stayed 62. In the last two decades, space exploration___great contributions to weather forecasting. a. is making b. has made c. made d. makes 63. On July 20, 1969, Neil Armstrong ___down onto the moon, the first person ever set foot on another planet. a. was stepping b. stepped c. has stepped d. was step 64. When boarding the plane, many passengers were annoyed because they ________ waiting in the airport for three ad a half hours. a. are b. were c. have been d. had been 65. By the end of this year, Tom ________English for three years. a. will be studying b. has studied c. will have studied d. has been studying 66. They ________ this course by next June. a. have finished b. will finish c. are going to finish d. will have finished 67. She will go abroad as soon as she________ this English course. a. has completed b. will complete c. will have completed d. completed 68. I / have/ wonderful time/ Da Lat/ moment A. I was having a wonderful time in Da Lat in the moment. B. I am having a wonderful time in Da Lat at the moment. C. I had a wonderful time in Da Lat at the moment. D. I am having a wonderful time at Da Lat in the moment. 69. I / already / visit / Xuan Huong Lake / Prenn Waterfall/ places of interest. A. I have already visit Xuan Huong Lake, Prenn Waterfall and some places of interest. B. I have already visited Xuan Huong Lake, Prenn Waterfall and some places of interest. C. I was already visiting Xuan Huong Lake, Prenn Waterfall and some places of interest. D. I am already visiting Xuan Huong Lake, Prenn Waterfall and some places of interest. 70. Last night/ I / visit/ Da Lat market / buy / lot/ souvernirs . A. Last night I visit Da Lat market and buy lots of souvernirs. B. Last night I was visiting Da Lat market and buying lots of souvenirs. C. Last night I visited Da Lat market and bought a lot of souvenirs. D. Last night I have visited Da Lat market and bought a lot of souvenirs.