ket核心語法：could you please open the door

1. 過去進(jìn)行時

談?wù)撨^去某個時候正在發(fā)生的事情

I was playing football at 3:30 yesterday.

談?wù)撨^去同時發(fā)生的兩件事

He was doing homework while his sister was watching TV.

過去進(jìn)行時和一般過去時出現(xiàn)在同一個句子中：

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，could可以作為can過去式使用

can/can't表示能力，用于當(dāng)前時間

I canhelp you.((我可以幫助你)

could/couldn't過去時用于表示能力。

can/can't用于當(dāng)前時間的表示概率

This can't be true.(這不可能是真的)

could表示概率，用于過去時，或用于現(xiàn)在時，但語氣沒有can強烈

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求。不同的是，它可以用于今天的請求could比can語氣更加委婉禮貌

Can you help me please?

Could you please open the door?