剑桥KET语法全概括（8）过去进行时+can/can't/could/couldn't

1. 过去进行时

• 用于谈论过去某个时间正在发生的事情I was playing football at 3:30 yesterday.

• 用于谈论在过去某个时间同时发生的两件事He was doing homework while his sister was watching TV.

• 过去进行时与一般过去时在同一个句子里出现的情况：I was doing homework when my sister came to talk to me.Someone knocked at the door while my mother was cooking.

• 否定句、疑问句的表达方式:He was not/wasn't working.They were not/weren't speaking to each other.Was he working? Yes, he was/No, he wasn't.Were they speaking to each other? Yes, they were/No, they weren't.

2. can/can't/could/couldn't

• 在有些时候，could可以作为can的过去式使用

• can/can't表示能力，用于现在时I can help you.（我能帮助你）

• could/couldn't表示能力，用于过去时，。比较：I couldn't come yesterday.（我昨天不能来）I could have come yesterday.（我昨天能来，但是没来）

• can/can't表示可能性，用于现在时This can't be true.（这不可能是真的）

• could表示可能性，用于过去时，或者用于现在时但语气没有can强烈He couldn't go there without me.（他不可能不带我一起去）

• can/could还可以在现在时中用于请求，区别在于could比can语气更委婉客气Can you help me please?Could you please open the door?

推荐阅读：

剑桥KET语法全概括（1）一般现在时+频率副词

剑桥KET语法全概括（2）现在进行时+have got

剑桥KET语法全概括（3）可数与不可数名词+many/much/a lot of/lots of/a few/a little

剑桥KET语法全概括（4）一般现在时与现在进行时的比较+too/enough

剑桥KET语法全概括（5）比较级与最高级+时间介词at,in,on

剑桥KET语法全概括（6）have to/must+主语代词/宾语代词的用法

剑桥KET语法全概括（7）一般过去时+祈使句