在請求語句里，couldn't比can't較委婉。在一般語句里，couldn't表過去時，can't表現(xiàn)在時。例句：I couldn't tell if he had been in a fight or had just fallen down.

相關(guān)例句

can't

1、I can't eat any more; I'm full up.

我不能再吃了，我已經(jīng)很飽了。

2、I don't want to leave, but I can't go on.

我不想離開，但我繼續(xù)不下去了。

3、I can't drink any more.

我不能再喝了。

4、Don't tell me you can't remember.

不要告訴我你記不起來了。

couldn't

1、Jamie e-mailed me to say he couldn't come

杰米給我發(fā)了電子郵件，說他不能來了。

2、I couldn't imagine why he would want to be alone with me

我想象不出為什么他會想和我獨(dú)處。

3、They put a screen in front of me so I couldn't see what was going on.

他們在我面前豎了一面屏風(fēng)，所以我看不到發(fā)生了什么事情。

4、I couldn't get back to sleep.

我再也睡不著了。