Cho số thực dương a,b,c thỏa mãn a+b+c=3. Chứng minh rằng

Một con quay là ghép của 2 khối trụ được xếp chồng lên khối nón. Thiết diện qua trục có dạng như hình vẽ bên. Khối trụ thứ nhất có bán kính đáy r1, chiều cao h1; khối trụ thứ hai có bán kính đáy r2, chiều cao h2; khối nón có bán kính đáy r3, chiều cao h3. Biết rằng r2 = 2r1 = 2r3; h3 = 2h2 = 4h1 và thể tích của con quay bằng 31 c m cubed Thể tích của phần khối nón bằng

A.  3 c m 3

B.  6 c m 3

C.  8 c m 3

D.  4 c m 3

2.  She/ be/ to Dubai/ three times/ year.

A. She is to Dubai three times this year.                                B. She is to Dubai three times year.

C. She has been to Dubai three times year.                          D. She has been to Dubai three times this year.

3.  Many/ tourists/ visit/ Hanoi/ year.

A. Many tourists visited Hanoi every year.                            B. Many tourists visit Hanoi every year.

C. Many tourists will visit Hanoi every year.                         D. Many tourists has visited Hanoi every year.

4.  The first/ sport competition/ held/ Greece/ 776 B.C.

A. The first sport competition is held in Greece in 776 B.C.

B. The first sport competition was held in Greece in 776 B.C.

C. The first sport competition is held on Greece in 776 B.C.

D. The first sport competition was held on Greece in 776 B.C.

33. I / not / visited / museum / three months.

A. I haven't visited the museum three months ago.

B. I haven't visited the museum for three months.

C. I didn't visited the museum for three months.

D. I haven't visited the museum three months ago.

34. Ms Linda / beautiful photos / few days ago.

A. Ms Linda took many beautiful photos a few days ago.

B. Ms Linda took much beautiful photos a few days ago.

C. Ms Linda took many beautiful photos few days ago.

D. Ms Linda took much beautiful photos few days ago.

35. The students / arrived / because / traffic jam.

A. The students arrived late because the traffic jam.

B. The students arrived late because of the traffic jam.

C. The students arrived lately because the traffic jam.

D. The students arrived lately because of the traffic jam.

36. I / eat / fruits / because / they / green.

A. I can't eat these fruits because of they are green.

B. I can't eat this fruits because of they are green.

C. I can't eat these fruits because they are green.

D. I can't eat this fruits because they are green.

Choose the sentences which is closest in meaning to the sentence above.

37. Classical music and modern music are different.

A. Classical music is like modern music.

B. Classical music is different from modern music.

C. Classical music is the same as modern music.

D. Classical music is  same as modern music.

38.  My parents usually watch TV in the evening.

A. My parents never watch TV.

B. In the evening, my dad and my mom usually watch TV.

C. In the evening, my mom and my dad clean our house.

D. My parents always watch TV in the evening.

39. I have never seen such a beautiful girl before.

A. She is the most beautiful girl I have seen.

B. She is the most beautiful girl I have saw.

C. She is the most beautiful girl I saw.

D. She is most beautiful girl I have saw.

40. Tom bought that book yesterday.

A. That book was bought yesterday by Tom.

B. That book was bought by Tom yesterday.

C. That book yesterday was bought by Tom.

D. That book was bought yesterday.