如果想用英语来谈论做一件事情是出于义务，那么则可以使用情态动词：“must” 必须、“mustn’t” 必须不；“have to” 有义务、 “don't have to” 没有义务。此外，也可以用 “need to” 、“need not” 或 “needn't” 来谈论是否有必要做一件事情。这些情态动词怎么用？做测验题，考一考自己是否真正掌握了这些表示义务和必要性的情态动词。

1. Complete the sentence so it expresses obligation.
You _______ attend the meeting scheduled for midday in the Great Hall.

a) would

b) may be

c) can

d) have to

2. Complete the sentence so it expresses necessity.
You _______ apply for your visa at the American Embassy.

a) need to

b) are able to

c) could

d) may

3. Complete the sentence so it expresses obligation.
All humans _______ have regular and sufficient sleep if they want to be healthy.

a) would

b) must

c) will

d) can

4. Which of the following expresses no necessity?

a) You must take your books to school, otherwise you can’t learn.

b) You need to show your passport when you get to customs.

c) You needn’t have brought a coat – it wasn’t very cold.

d) He has got to take the entrance exam to be accepted to the university.

5. Complete the sentence so it expresses necessity.
If we want the band to be successful, _______ work hard.

a) we’ll have to

b) we’ll be able to

c) we could

d) we can

6. Complete the sentence so it expresses obligation.
You _______ respect your teachers.

a) would

b) could

c) should

d) can

7. Complete the sentence so it expresses necessity.
The lioness _______ hunt in order to feed her family.

a) has to

b) could

c) would

d) should

8. Which of the following expresses no obligation?

a) You should go and apologise to your sister.

b) You won’t need to buy a gallery pass – the exhibition is free.

c) You can’t work any longer – we’re locking the office now.

d) You shouldn’t go to work today – you look very sick.

答案

1) d, 2) a, 3) b, 4) c, 5) a, 6) c, 7) a, 8) b.