can和be able to的区别.ppt

和 用法的区别
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can
be able to
.
1
它们用法上的不同主要体现在以下几方面:
1. can只有两种时态, 即can 和could;而be able to 有多种时态, 如was/were able to, will/shall be able to, have/has been able to等。
.
I’ll be able to drive the car in a week.
Through his diligent work, the deaf-mute has been able to read and write in a sign language.
.
2
able to，而不能用can。can 和be able to , be able to 则主要指具体做到了某件事的能力.
I can swim.
I am able to swim.
(√) (√)
All the people could escape from the big fire in time.
All the people were able to escape from the fire in time.
(×)(√)
.
3
，be able to不能。can的这种用法主要用于疑问句和否定句。其肯定形式是must be。
.
Somebody is knocking at the door. Who can it be?
It can’t be our teacher who is knocking at the door.
It must be our teacher who is knocking at the door.
.
4
4．can 可以表 “允许”, 与may可以互换, 此时不能用be able to 代替。如： “Can / May I sit here？” 由于may not 有两个意思, 即 “不可能” 和 “不许可”, 在口语中，表达这两种不同的含义是通过句重音来解决的。
He may not go home this weekend.
He may `not go home this weekend. (I don’t permit him