③ 二者的否定意义不大相同。如：

You mustn't go. 你可不要去。

You don't have to go. 你不必去。

④ 询问对方的意愿时应用must。如：

Must I clean all the room?

2 1)Can you speak English?

__________________________________________________ can表示能力(如体力和脑力方面)，意为“__________”等can表示能力时，还可用be able to代替。如：

I'll not be able to come this afternoon.

2)表示请求或允许，多用在口语中，意为“__________”等。

— Can/Could I go now?

— Yes, you can.(回答语中不能用could)

3) 表示惊异、怀疑、不相信的态度。(主要用在否定句、疑问句或惊叹句中)

Can this be true? ______________________

How can you be so careless! ___________________

This cannot be done by him. __________________

4)在变否定句时，直接在后加上“not”,可缩写成_________或___________, 但不能写成cann’t。例如：

(变成否定句) He can swim. → _______________________

3  ought意思是______________后面跟带有 to 的动词不定式否定式为_________________。(C级)

You ought to read these books if you want to know how to repair the motorcar.

____________________________________________

You ought to bring the child here.

_____________________________________________

You ought not to walk alone at night. _____________________________________________

注意： ought to和should的区别：

1.ought to语气略强。     2.should较常用。

3.ought to在美国英语中用的很少，而should却相当常用。

4.ought to属正式用语。

练一练：(C级)

1The man in the office____________be Mr. Black because he went home

just now.

A. mustn’t   B. may not    C. can’t      D. needn’t

2---Can you go surfing with us this afternoon?

----I’d like to , but I ________ look after my sister at home , because my mother is ill.

A. need      B. must      C. have to      D. should

3----Can I take this book out of the reading room?