如果想用英語來談論做一件事情是出于義務，那么則可以使用情態動詞：“must” 必須、“mustn’t” 必須不；“have to” 有義務、 “don't have to” 沒有義務。此外，也可以用 “need to” 、“need not” 或 “needn't” 來談論是否有必要做一件事情。這些情態動詞怎么用？做測驗題，考一考自己是否真正掌握了這些表示義務和必要性的情態動詞。

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.