2 比较can 和be able to 1)can could 表示能力,可能 , 只用于现在式和过去式.be able to可以用于各种时态. They will be able to tell you the news soon. 他很快就能告诉你消息了. 2)只用be able to a. 位于助动词后. b. 情态动词后. c. 表示过去某时刻动作时. d. 用于句首表示条件. e. 表示成功地做了某事时.只能用was/were able to. 不能用could. He was able to flee Europe before the war broke out. = He managed to flee Europe before the war broke out. 注意:could不表示时态 1)提出委婉的请求.(注意在回答中不可用could). --- Could I have the television on? --- Yes, you can. / No, you can't. 2)在否定.疑问句中表示推测或怀疑. He couldn't be a bad man. 他不大可能是坏人. 【查看更多】
