五、should/ought to/could have done与should/ought to/could do的区别

形式 用法 should/ought to have done 表示本来应该做而没有做某事 could have done 表示本来能做而没有做某事 should/ought to do 表示应该做某事，一般指还没有发生 could do 表示过去的能力 　　

　　You should have done your homework last night，but you went to the cinema with your friends.

　　昨天晚上你本应该做作业，但你和你的朋友去看电影了。

　　I could have helped you，but I was too busy then.

　　我本可以帮助你的，但那时我太忙了。

　　You ought to study hard from now on.

　　从现在起，你应该努力学习。

　　She could speak English when she was three years old.她三岁时就会说英语。

　　即时跟踪　用适当的情态动词填空

　　1.When we worked in the same office ，we would often have coffee together.

　　2.Look！Tom is too sleepy to work.He must have stayed up watching TV last night.

　　3.You shall die if you disclose all the state secrets to the foreigners.

　　4.I should have helped him when he was in trouble，but I was away at that time.

　　5.English is a language that many people around the world may not speak perfectly but can at least understand.

　　Ⅰ.用适当的情态动词填空

　　1．George can't have gone too far.His coffee is still warm.(2016·浙江)

2．It was really annoying；I couldn't get access to the data bank you had