Section Ⅳ　Grammar & Writing

　　情态动词

　　阅读下列句子，体会黑体部分的用法

　　1．They could go anywhere they wished.

　　2．We could see the sun setting behind the white pagoda.

　　3．We shouldn't waste a drop of water.

　　4．It may be true.

　　5．He might have some fever.

　　6．Since it is raining，we have to stay indoors.

　　7．We must learn English well.

　　8．Must you listen to the loud music at night?

　　情态动词表示说话人对某一动作或状态的态度，但本身词义不完全，不能单独作谓语动词，必须和动词原形连用。情态动词没有人称和数的变化。每一个情态动词都有自己的具体含义和特点。

　　1．can(could)

　　(1)表示能力(此时could为过去式)

　　He can use the computer skillfully now，but he couldn't last year.

　　他现在能熟练使用电脑了，但去年他不会。

　　(2)表示推测(用于否定句和疑问句中)

　　①That can't be Mary.She's in hospital.

　　那不可能是玛丽。她住院了。

　　②Someone is knocking at the door.Who can it be?

有人在敲门，可能是谁呢？