1704926740
1704926741
Could you run as fast as you do now？那时你能跑得像现在这样快吗？
1704926742
1704926743
（也可说：Were you able to run as fast as you do now?）
1704926744
1704926745
She couldn’t understand his state of mind．她不能理解他的心理状态。
1704926746
1704926747
（也可说：She wasn’t able to understand his state of mind.）
1704926748
1704926749
但be able to可以更明确地表示时间关系（可用于多种时态）：
1704926750
1704926751
Will you be able to join us？你能参加我们的活动吗？
1704926752
1704926753
We won’t be able to catch that train．我们赶不上那班火车。
1704926754
1704926755
She said she wouldn’t be able to go with us．她说她无法和我们一道去。
1704926756
1704926757
I haven’t been able to do that up till now．到现在为止我还没能这样做。
1704926758
1704926759
She said she hadn’t been able to get in touch with them．她说她还未能和他们联系上。
1704926760
1704926761
be able to还可和may, might, should等情态动词一起用：
1704926762
1704926763
I may be able to get a ticket for you．我可能能给你弄到一张票。
1704926764
1704926765
She might be able to help us．她有可能帮我们的忙。
1704926766
1704926767
You should be able to understand this．你应当能理解这一点。
1704926768
1704926769
She wouldn’t be able to accomplish all this alone．她独自一人是不可能完成这一切的。
1704926770
1704926771
be able to还可用在非谓语形式中：
1704926772
1704926773
She hoped to be able to do something for you．她希望能为你做点儿什么。
1704926774
1704926775
He felt bad for not being able to lend a hand．他因不能帮忙感到遗憾。
1704926776
1704926777
She watched all this happen, not being able to do anything．她眼看着这一切发生却毫无办法。
1704926778
1704926779
在上面这些情况下，can和could都是没法用的。
1704926780
1704926781
除了表示“能够”，can, could还有一些其他用法，是不能用be able to代替的。这些用法主要是表示：
1704926782
1704926783
可能性（可译为“可以”、“可能”）：
1704926784
1704926785
We can call for you at nine．我们可以9点钟来叫你。
1704926786
1704926787
I’m like that—you can’t alter me．我就是这样，你不可能改变我。
1704926788
1704926789
He said he couldn’t come．他说他不可能来。
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