语法复习十一：助动词与情态动词_高考语法

语法复习十一：助动词与情态动词

　　3、must的基本用法

　　(1)must表示必须、应该之意，其否定式 must not，缩写形式为 mustnt，表示不应该，不准、不许可或禁止之意，如：We must study hard and make progress every day. You mustnt touch the fire. (2)对以must提出的疑问句，如作否定回答时，要用neednt或用dont (doesnt) have to (不必)来回答，而不用mustnt，因为mustnt表示的是禁止或不许可之意，如：---- Must we finish the work tomorrow? ---- No, you neednt (dont have to), but you must finish it in three days. (3)在肯定句中must可以表示推测，表示一定或必定之意，如：---- Whose new bike can it be? ---- It must be Liu Dongs. I know his father has just bought him a new one.

　　4、can, could, may, must后接完成式的用法

　　(1)can, could后接完成式的用法：①在否定句或疑问句中表示对过去发生过的事情的怀疑或不肯定的态度，Could he have said so? ②在肯定句中，可以表示过去可能做到而实际并没做到的事情，有劝告或责备的语气。如：---- When did you answer her letter? ---- Only yesterday. ---- Its too late. You could have answered it earlier, I am sure. (2)may, might后接完成式的用法 ①表示对过去某事的推测，认为某一件事情在过去可能发生了。如果使用might，语气就比较婉转或更加不肯定，如：Mary might have learned some Chinese before. ②可以表示过去本来可以做到而实际没有做到的事情，有劝告或责备的语气，如：You didnt do the work well that day. You might have done it better. (3)must后接完成式的用法：表示对过去某事的推测，认为某事在过去一定做到了，如：Liu Dong isnt in the classroom. He must have gone to the library.