做。 He could have passed the exam, but he was too careless. 本来他能够通过考试，但是他太粗心。

5. "may+have+done"表示对发生过去的事情的推测，意思是"可能已经"或"也许已经"，用于肯定句中。

-What has happened to George? -I don't know. He may have got lost.

-乔治发生了什么事？--我不知道，他可能迷路了。

"might+have+done"表示对过去事情的推测，might与may意思相同，但可能性更小。多用于虚拟语气结构中。

1). He might have given you more help, even though he was busy. (MET90) 他或许会多给你一些帮助，即使他很忙。

2). She might have achieved greater progress, if you had given her more chances. 如果你多给她点机会，她可能已经取得更大的成绩。

6."should+have+done"意思是"本来应该做某事，而实际没做。" "shouldn't+have+done"表示本来不应该做某事，而实际做了。含有指责对方或自责的含意。

1). Tom, you are too lazy. The work should have been finished yesterday. 汤姆，你太懒惰了，这项工作本来应该昨天就做完的。

2). Look, Tom is crying. I shouldn't have been so harsh on him. 看，汤姆哭了，我本来不应该对他如此严厉。

7. "ought to+have+done"表示过去应该做而实际并没有做，译成"理应做......"，往往表示遗憾。与"should+have+done"用法基本一样。

例1. (2015•北京)-Can't you stay a little longer?

-It's getting late. I really _____go now, My daughter is home alone.

A .may B .can C . must D .dare

例2. (2015•重庆) You__________ be Carol. You haven't changed a bit after all these years.

A. must B. can C. will D. shall

例3. (2015安徽安庆一中月考) If you were older I ________ you to go there yesterday.

A .will allow B. should allow C. would have allowed D. had allowed

例4. (2014北京海淀二模) If I ______the project earlier, I would be enjoying myself on the beach now.

A. might finish B. finished C. had finished D. would have finished

例5. (2015北京海淀一模)-What do you think of the Huawei P7?

-Terrific. I would buy one if I ________ an iPhone 6 Plus last year.

A. didn't buy B. don't buy C. hadn't bought D. haven't bought