He started late,but he---catch the 8'clock bus.

问题描述:

He started late,but he___catch the 8'clock bus.
A.could
B.was able to
C.might
D.ought to
could和 was able to有什么区别呢?这道题好迷糊,觉得好像都可以.
1个回答 分类:英语 2014-11-16

问题解答:

我来补答
选B,could不表示时态,所以选was able to,详细解释如下:
1)can could 表示能力;可能 (过去时用could),
只用于现在式和过去式(could).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.
can用于表示“能力”时是指现在的能力,过去或将来的能力通常用was/were able to或will/shall be able to表示.
eg. She was able to go to school yesterday.
Soon she will be able to swim a quarter of a mile.
Can的过去式形式could也可用于表示泛指过去的能力.如:
I could read when I was four.
但不能用于表示特定的某一过去能力,如不能说:
*He could swim halfway before he got tired.
He was able to swim halfway before he got tired.
上述这种用法的区别不存在于否定句中.在否定句中,couldn’t与was/were not able to 可以互换使用.
eg. I couldn’t see him again before he left.
I wasn’t able to see him again before he left.
另外,要说一个阶段延续至今的能力,可用have/has been able to表示.
eg. John has been able to swim for many years.
注意的一点是:can也可以用于表示“许可”.它可以表示现在许可或将来许可,过去许可用could表示,此时一律不能用be able to的某种形式替换.
 
 
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