ket核心語(yǔ)法：could you please open the door

1. 過(guò)去進(jìn)行時(shí)

談?wù)撨^(guò)去某個(gè)時(shí)候正在發(fā)生的事情

I was playing football at 3:30 yesterday.

談?wù)撨^(guò)去同時(shí)發(fā)生的兩件事

He was doing homework while his sister was watching TV.

過(guò)去進(jìn)行時(shí)和一般過(guò)去時(shí)出現(xiàn)在同一個(gè)句子中：

Iwas doing homework when mysister cameto talk to me.

Someone knocked at the doorwhilemy mother was cooking.

表達(dá)否定句、疑問(wèn)句：

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

有時(shí)，could可以作為can過(guò)去式使用

can/can't表示能力，用于當(dāng)前時(shí)間

I canhelp you.((我可以幫助你)

could/couldn't過(guò)去時(shí)用于表示能力。

can/can't用于當(dāng)前時(shí)間的表示概率

This can't be true.(這不可能是真的)

could表示概率，用于過(guò)去時(shí)，或用于現(xiàn)在時(shí)，但語(yǔ)氣沒(méi)有can強(qiáng)烈

He couldn't go therewithout me.(他不能不帶我一起去)

can/could它也可以用于今天的請(qǐng)求。不同的是，它可以用于今天的請(qǐng)求could比can語(yǔ)氣更加委婉禮貌

Can you help me please?

Could you please open the door?