ket的语法：could you please open the door

1. 过去进行时

用来谈论过去某一时间正在发生的事情。

I was playing football at 3:30 yesterday.

用来讨论过去某一时间同时发生的两件事

He was doing homework while his sister was watching TV.

过去的情况和过去的情况发生在同一句话中：

Iwas doing homework when mysister cameto talk to me.

Someone knocked at the doorwhilemy 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

有时，could可以作为can过去式使用

can/can't表现能力，用于当今时代。

I canhelp you.(我可以帮助你)

could/couldn't在过去的时候，表达能力。

can/can't表示概率，用于当今时代。

This can't be true.(这个不可能是真的)

could表示概率，用于过去，或者用于现在，但是语气没有can强烈

He couldn't go therewithout me.(他不可能不带我一起去)

can/could也可用于今天的请求，不同之处在于，could比can语调更加委婉客气

Can you help me please?

Could you please open the door?