1. must。由You haven't changed a bit after all these years可知，前句意为"你一定是卡罗尔"，故选must。must表示推测时意为"肯定，一定"，用于肯定句中，语气最强。

2. may。由but及后一分句中的later you'll be grateful you did it可知，设空处表示推测，意为"或许可能"，故选may。should表示推测时意为"按理应该"。

3. can。句意为"尽管你可能会在伦敦找到便宜货，但总的来说那不是一个购物便宜的地方"，can在此表示可能性。

4. might。句意为"生活是难以预料的，即使一贫如洗的人或许会成为最富有的人"。might表推测时语气最弱，意为"或许"。

5. can't。由He's busy可知，"哈丁先生现在不可能见你"。can't表示"不可能"，语气较强。

考点三："情态动词+ have done"结构

【考例】

选用括号内合适的内容填空。

1. I ________ (needn't / couldn't) have worried before I came to the new school, for my classmates here are very friendly to me. (天津2015)

2. -Sorry, Mum! I failed the job interview again.

-Oh, it's too bad. You ________ (would / should) have made full preparations. (福建2015)

3. Harry is feeling uncomfortable. He ________ (would / must) have drunk too much at the party last night. (辽宁2013)

【点拨】

1. needn't。由my classmates here are very friendly to me可知，"我来新学校之前本来没必要担忧"。needn't have done表示"本没必要做某事（却做了）"。

2. should。由Oh, it's too bad可知，"你本应该做充分的准备"。should have done表示"本来应该做某事（却没做）"。shouldn't have done表示"本来不应该做某事（却做了）"。

3. must。由Harry is feeling uncomfortable可知，"他昨晚在聚会上一定喝了太多酒"。must have done表示"一定做了某事"。否定句中用can't / couldn't have done。