過(guò)去進(jìn)行時(shí)的主要用法
1.表示過(guò)去某一時(shí)間內(nèi)(正在)進(jìn)行的動(dòng)作
　如：I was doing my homework at 9 p.m. last Sunday.
2.表示一動(dòng)作正在進(jìn)行時(shí)，另一動(dòng)作同時(shí)正在進(jìn)行.
　(1)用while連接(while只接doing)
　例:My mother was cooking while I was doing my homework.(可以持續(xù)動(dòng)作時(shí)態(tài)一致)
　(2)when表示(when可以接doing或did，when后動(dòng)作時(shí)間長(zhǎng)，用doing，時(shí)間短，用did)
　例:I was doing my homework when my mother came in.(間接表達(dá)了具體時(shí)間)
3.重復(fù)的動(dòng)作
　When he worked here, John was always making mistakes.
4.表示過(guò)去將要發(fā)生的動(dòng)作
　She told us Mr.Lee was arriving here.
5.用于故事，以提供其時(shí)間背景
6.表示禮貌