1、過去進(jìn)行時(shí)（Past Continuous）

描述一個(gè)過去的事件被打斷了。To be (過去式) + 現(xiàn)在分詞ing。

The boys were riding their bikes, when it started raining.

He was studying when I called. (過去進(jìn)行時(shí)描述之后，后面的動(dòng)詞用簡(jiǎn)單過去)

2、現(xiàn)在進(jìn)行時(shí)（Present Progressive/ Continuous）

描述一個(gè)現(xiàn)在正在進(jìn)行的事情，眼下正在發(fā)生的事。To be(現(xiàn)在式) +現(xiàn)在分詞ing.

What is Sally doing?

She is running through the park.

3、未來進(jìn)行時(shí)（Future Continuous）

描述一件將要發(fā)生的動(dòng)作被打斷了。will be +現(xiàn)在分詞ing

I will be cooking asparagus when you come back this evening.