1. 過去進行時

• 用于談論過去某個時間正在發(fā)生的事情I was playing football at 3:30 yesterday.

• 用于談論在過去某個時間同時發(fā)生的兩件事He was doing homework while his sister was watching TV.

• 過去進行時與一般過去時在同一個句子里出現(xiàn)的情況：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、疑問句的表達方式: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

• 在有些時候，could可以作為can的過去式使用

• can/can't表示能力，用于現(xiàn)在時I can help you.（我能幫助你）

• could/couldn't表示能力，用于過去時，。比較：I couldn't come yesterday.（我昨天不能來）I could have come yesterday.（我昨天能來，但是沒來）

• can/can't表示可能性，用于現(xiàn)在時This can't be true.（這不可能是真的）

• could表示可能性，用于過去時，或者用于現(xiàn)在時但語氣沒有can強烈He couldn't go there without me.（他不可能不帶我一起去）

• can/could還可以在現(xiàn)在時中用于請求，區(qū)別在于could比can語氣更委婉客氣Can you help me please?Could you please open the door?

推薦閱讀：

劍橋KET語法全概括（1）一般現(xiàn)在時+頻率副詞

劍橋KET語法全概括（2）現(xiàn)在進行時+have got

劍橋KET語法全概括（3）可數(shù)與不可數(shù)名詞+many/much/a lot of/lots of/a few/a little

劍橋KET語法全概括（4）一般現(xiàn)在時與現(xiàn)在進行時的比較+too/enough

劍橋KET語法全概括（5）比較級與最高級+時間介詞at,in,on

劍橋KET語法全概括（6）have to/must+主語代詞/賓語代詞的用法

劍橋KET語法全概括（7）一般過去時+祈使句