過去時(shí)主要是指過去發(fā)生的動(dòng)作或存在的狀態(tài)
而過去進(jìn)行時(shí)表示過去某階段正在進(jìn)行的動(dòng)作,通常有時(shí)間暗示.
I did my homework yesterday .
I was doing my homework this time yesterday .While the pupils were doing classwork,their teacher returned.這個(gè)句子都沒有時(shí)間暗示，那為什麼要用Past continue tense呢？這里是屬于時(shí)間狀語從句中的過去進(jìn)行時(shí)，當(dāng)小學(xué)生們當(dāng)時(shí)正在做功課的時(shí)候，老師返回來了。while/when/as引導(dǎo)的時(shí)間狀語從句如果是長時(shí)間動(dòng)詞，主句是短時(shí)間動(dòng)詞，長時(shí)間動(dòng)作用過去進(jìn)行時(shí)，短動(dòng)作用一般過去時(shí)。While /When /As she was walking on the street, it began to rain.還有這樣的句子， I was cooking whensomeoneknocked at the door.