Section Ⅳ　Grammar & Writing

　　情态动词＋have done　

　　阅读下列句子，体会黑体部分的用法

　　1．But in China，the idea of the dragon may have come from the alligator.

　　2．You might have given your parents more help earlier.

　　3．He can't have forgotten it，for he talked about it yesterday.

　　4．You ought to/should have done the job more carefully.

　　5．You oughtn't to/shouldn't have asked such a foolish question.

　　情态动词是高中英语语法的一个重要部分，而"情态动词＋have done"结构则是对此知识点考查的一个重点和难点。该结构一般有两个主要用法：一是表示对过去发生的动作或状态的推测，二是表示对过去发生的动作的遗憾或责备。

　　一、对过去的推测

　　1．must have done表示对过去发生的事情的肯定推测，意为"一定做过......"，只用于肯定句中。

　　It must have rained last night，for the road is quite muddy.

　　昨晚一定下雨了，因为路面很泥泞。

　　2．can/could have done表示对过去发生事情的推测，常用于否定句，意为"不可能做过某事"和疑问句，意为"可能做过......吗？"

　　Mr.Smith can't have gone to Beijing，for I saw him in the library just now.

　　史密斯先生不可能去北京了，我刚才还在图书馆见过他。

　　There is nowhere to find them.Where can they have gone?

到处找不到他们，他们可能到什么地方去呢？