1．can和could (could是can的过去式，语气更委婉)

　　(1)表示能力。

　　He can use the computer skillfully now, but he couldn't last year.

　　他现在能熟练使用电脑了，但去年他不会。

　　(2)表示可能性(肯定句中表示"一时的可能性"), 可译为"有可能；有时会"。

　　Training by oneself in a gym can be highly dangerous.

　　一个人在体育馆训练有时会很危险的。

　　(3)表示许可。

　　-Can/Could I have a look at your new pen?

　　-Yes, you can./No, you can't.

　　--我可以看一看你的新钢笔吗？

　　--可以。/不可以。

　　[名师点津]　can 表示允许时，在疑问句中用 could 更委婉，在回答中一律用 can。

　　(4)can/could在否定句、疑问句中表示推测或怀疑，译为"可能"。

　　That can't be Mary - she's in hospital.

　　那不可能是玛丽--她在住院。

　　Someone is knocking at the door. Who can it be?

　　有人在敲门，可能是谁呢？

　　(5)can't与enough或too连用，表示"再......也不为过"。

　　You can't be careful enough.

　　你再细心也不为过。

　　(6)can与be able to的区别。

　　can表示"能力"时，只有can与could两种形式，仅表示具备的能力，不说明是否实施了努力。

　　be able to表示"能力"时，可以用于各种时态， be able to 用于过去时态表能力时，侧重指经过努力而成功做到某事。

　　The fire spread through the hotel very quickly, but everyone was able to get out.

　　大火在整个宾馆内蔓延开来，但每个人都成功逃出来了。

　　[即时演练1]

　　选词填空：can, could, couldn't, be able to

　　①(2016·天津高考改编)It was really annoying; I couldn't get access to the data bank you had recommended.

　　②(2015·浙江高考改编)It was so noisy that we couldn't hear ourselves speak.

③(2014·大纲卷改编)Although you can find bargains in London, it's not generally a cheap