(4)could的否定式与比较级连用表示最高级。

　　No one could be more generous; he has a heart of gold.

　　没人比他更慷慨；他有一颗金子般的心。

　　(5)could have done表示"可能已经......"。此外，它还可以表示"本能够做某事(而没有做)"，暗含惋惜之情。

　　You could have done it well, but you were too careless.

　　你本可以做好的，但是你太马虎了。

　　Where could she have gone last night?

　　她昨晚可能到哪里去了呢？

　　2．should的用法

　　(1)表示劝告和建议，意为"应该"。此时ought to比should语气要强。

　　You should/ought to put more effort into your work.

　　你应该更加努力地工作。

　　(2)表示推测：用于肯定句，表示按常规、常理的推测，意为"按理说应该"。

　　He left Paris in the morning. So he should arrive here by supper time.

　　他早上离开巴黎， 因此他晚饭前应该能到。

　　(3)表示惊讶、意外等情绪，意为"竟然"。

　　It is strange that such things should happen in our school.

　　真奇怪，这样的事情竟然在我们学校发生了。

　　(4)should (not)＋have done。

　　should have done sth.表示"本应该做某事，但事实上却没有做"； shouldn't have done sth.表示"本不该做某事，但事实上做了"。

　　You should have got up earlier.

　　你本应该早点起床的。

　　You shouldn't have told him about it.

　　你本不该把这件事告诉他的。

　　3．would的用法

　　(1)表示意愿，在陈述语气和虚拟语气中都可用。

　　I told Peter that I would go along with him.

　　我告诉彼得我要跟他一块去。

　　(2)表示请求、建议等，would比will委婉客气。在疑问句中用于第二人称。

　　Would you please tell me the way to the nearest bus­stop?

　　你可以告诉我去最近的公共汽车站的路吗？

　　(3)表示习惯，意为"总是，习惯于"。与used to相比，would表示过去重复、习惯性动作；而used to则强调过去与现在的对比。

　　Last year our English teacher would tell us stories in English after class.

　　去年我们的英语老师常常课后给我们用英语讲故事。

　　He used to spend all his money on food and drink; now he lives a simple life.

　　他过去把钱都花在吃喝上，现在他过着简朴的生活。

　　集中演练2

　　选词填空：could, should, would

　　①We should always lend a hand to those who are less fortunate than we are.

　　②I don't like fish, so I would not eat it unless I was extremely hungry.

　　③It could not be the vocabulary that caused you the problem in the exercise because you know a lot of words.

④You can't imagine that a well­behaved gentleman should be so rude to a lady.