Giải bài toán cổ sau đây bằng cách lập hệ phương trình:

Một đàn em bé tắm bên sông

Lấy ống làm phao, nổi bềnh bồng

Hai chú một phao, thừa bảy chiếc

Hai phao một chú, bốn người không

Hỡi người thạo tính, cho hỏi thử

Mấy phao, mấy chú, tính cho thông?

Câu If:

1) My mother buys that car for him. He will be happy.

--> If

2) They don't buy that car because it is so expensive.

--> If

3) Mary is lazy, so she doesn't pass her exam.

--> If

4) The weather is very cold, and we won't take a bath.

--> If

5) She is so busy and she doesn't have dinner.

--> If

6) Our teacher doesn't come to class because he does something.

--> If

7) I don't enjoy the film because it is not exciting.

--> If

8) Because they come here late, they don't see Mr. John.

--> If

9) My sister finishes the test easily because she is very intelligent.

--> If

10) My father is busy and he never watches TV.

--> If

11) Go out or you will be bitten.

--> If

12) Don't be late or you fail in the exam.

--> If

13) You won't win because he doesn't advised you.

--> If

14) Mary stays at home because she is sick.

--> If

Complete each blank with a suitable Preposition:

1) He speaks English like a native. He can give us advice ... how to improve our pronunciation.

2) Hoa often helps Na ... her written assignments.

3) Why don't you work harder ... the project? We have only two days left to complete it.

4) The TV repairman will be here ... five minutes.

5) People throughout the world must work together to look ... the environment.

6) If you go ... leaving the lights on all day, you will have an enormous electricity bill to pay ... the end of this month.

7) Have you seen my little sister? I've been looking ... her ... two hours.

8) Travelling ... public transport will reduce the amount of exhaust fume from cars and motorbikes.

9) I spend $16 a month ... fares and I have to pay $32 ... lighting.

10) What is the purpose ... visit ... our country?

11) We are interested ... the shortage of fresh water ... the world's population.

12) The cost of living in Vietnam is low compared ... Singapore.

13) Did children account ... 45 percent of the total population affected by the tsunami?

14) This toilet roll is finished. It should be replaced ... a new one.

15) The head of the household should tell each family member to be aware ... saving energy.

16) Instead ... buying energy-saving lights, we should concentrate ... a more economical use of electricity.

17) He is good ... fixing wooden objects, but he is bad ... building with bricks.

18) This electrical appliance will not work ... electricity.

19) Look ... this enormous telephone bill before leaving ... work, darling. I can't believe in my eyes.

20) If you've got a cough, you should try to cut ... the number of cigarettes you smoke.

Complete the sentences. Use the right tense form of the phrasal verbs: go off (1); go off (2); turn off; turn on; set off; cut off; come off; get off; see off; take off.

1) You can ... your jacket if you like.

2) We forgot to pay the bill and our electricity was ... .

3) Monica didn't want to ... the bus because it was raining.

4) ... the machine and give it time to heat up.

5) You don't need to come to the station to ... me ... . I'll be fine on my own.

6) You must drink it up until two weeks or it will ... .

7) Oh bother! One of my button has ... .

8) I set the alarm for 7 a.m before going to bed last night, but this morning it didn't ... .

9) Remember to ... the lights before leaving for work.

10) We decided to ... early the next day to avoid the rush hour traffic.

Vật sáng AB đặt trước một thấu kính, vuông góc với trục chính Δ, A nằm trên trục chính. Cho biết ảnh A'B' của AB qua thấu kính ngược chiều với AB và cao gấp hai lần AB, khoảng cách AA' = 45 cm. Dùng phép vẽ hãy xác định vị trí quang tâm O và các tiêu điểm F, F' của thấu kính rồi dùng các phép tính hình học để tìm tiêu cự f của thấu kính.

Complete each blank with a suitable Preposition:

1) He speaks English like a native. He can give us advice ... how to improve our pronunciation.

2) Hoa often helps Na ... her written assignments.

3) Why don’t you work harder ... the project? We have only two days left to complete it.

4) The TV repairman will be here ... five minutes.

5) People throughout the world must work together to look ... the environment.

6) If you go ... leaving the lights on all day, you will have an enormous electricity bill to pay ... the end of this month.

7) Have you seen my little sister? I’ve been looking ... her ... two hours.

8) Travelling ... public transport will reduce the amount of exhaust fume from cars and motorbikes.

9) I spend $16 a month ... fares and I have to pay $32 ... lighting.

10) What is the purpose ... visit ... our country?

11) We are interested ... the shortage of fresh water ... the world’s population.

12) The cost of living in Vietnam is low compared ... Singapore.

13) Did children account ... 45 percent of the total population affected by the tsunami?

14) This toilet roll is finished. It should be replaced ... a new one.

15) The head of the household should tell each family member to be aware ... saving energy.

16) Instead ... buying energy-saving lights, we should concentrate ... a more economical use of electricity.

17) He is good ... fixing wooden objects, but he is bad ... building with bricks.

18) This electrical appliance will not work ... electricity.

19) Look ... this enormous telephone bill before leaving ... work, darling. I can’t believe in my eyes.

20) If you’ve got a cough, you should try to cut ... the number of cigarettes you smoke.

Make a cross on the correct answer A, B, C or D in the following sentences:

1) Oh dear! How ... our household bills are! We can’t pay them.

A. heavy

B. enormous

C. small

D. low

2) In winter, heating ... for 50 percent of our electricity bill.

A. takes

B. occupies

C. accounts

D. costs

3) Energy can be collected by solar ... on cloudy days.

A. boards

B. panels

C. bars

D. sheets

4) If we don’t find ... sources of power, we will use up all the fossil fuels in the near future.

A. effective

B. efficient

C. natural

D. alternative

5) We want to use solar energy, ... it can’t be used on cloudy days.

A. but

B. so

C. because

D. however

6) Are wind power ... solar power new kinds of energy for future use?

A. and

B. or

C. with

D. but

7) He is always broke. He can’t afford neither luxuries ... basic necessities.

A. or

B. nor

C. and

D. but

8) Her husband bought not only 2 energy-saving light bulbs but ... one cheap washing machine last Sunday.

A. also

B. too

C. as well

D. some

9) You can’t have both of these products. Take one ... the other.

A. and

B. or

C. with

D. but

10) Ba really wants to buy new tables and chairs. ..., new furniture costs too much.

A. However

B. Therefore

C. But

D. So

11) If the TV always on in your house. You will not reduce the ... of electricity you use.

A. number

B. amount

C. much

D. plenty

12) “I suggest fixing the dripping faucet.” - “...”

A. We will.

B. Good idea.

C. Yes, please.

D. I’m afraid not.

13) Lan spoke English ... after she lived in England for several moths.

A. nature

B. natural

C. naturally

D. unnaturally

14) There’s nothing good on TV. Why don’t you turn it ...?

A. on

B. down

C. off

D. up

15) I’m trying to cut down ... the amount of driving I do to save energy.

A. off

B. to

C. out of

D. on

Give the correct form of the words in brackets:

1) A ... is a person who installs and repairs things such as water pipes, toilet, etc. (plumbing)

2) Water is going all over the floor because of the ... faucet. (drip)

3) You can ask that plumber for ... on how to repair the cracks in the water pipes. (advise)

4) To keep the air unpolluted, people ought to use ... energy to create electricity. (sun)

5) Here is the weather for tomorrow. Hanoi will be clear and ... (cloud)

6) ... are very demanding. They want products that are both of cheap and good quality. (consume)

7) We suggest ... the light bulb. It is broken. (replacement)

8) Recycled ... are of the same quality as those made from non-recycled material. (produce)

9) We must learn to save ... resources or life will be very bad for our children and our grandchildren. (nature)

10) In a few year’s time, our houses will be ... by the solar energy. (hot)

11) Since the world’s energy resources are limited, we must ... them. (conservation)

12) I’m pleased that my secretary solved the problem ... (effect)

13) The high cost of heating and ... prevents us from wasting electricity. (light)

14) With my small salary, I can’t afford basic ... like food, rent and fares. (necessitate)

15) There have been many ... in the field of electrical engineering. (innovate)

16) No doubt that there will be a great ... of food for the world’s population. (short)

17) Televisions, dishwashers, and freezers are electrical ... (apply)

18) If there is something wrong with the lights, ask an ... to look at it. (electric)

19) Can I borrow your ... dress? It’s been in the wardrobe for show since you bought it. (use)

20) ... bills are money for lighting, heating, etc. in your house. (house)

21) In many parts of the world where there are no fossil fuels, nuclear power is the only ... (alter)

22) Proper ... of a car’s engine will preserve its performance and value. (maintain)

23) The ... of the new computer system at our office won’t be finished until sometime next week. (install)

24) She is said to be ... . She isn’t relied on to do her job properly. (efficiency)

25) Rather ..., researchers forecast that oil might run out in 30 years. (pessimism)