过去进行时讲解（ 包括句型结构,用法,动词变化）

过去进行时表示在过去某一时刻或某一段时间内进行或发生的动作.其形式为was /were + V-ing.常与表示过去的时间状语连用,如：last night,last Saturday等；或者与when,while,as引导的过去时间状语连用.
基本用法
1.过去进行时的基本用法主要表示过去某一时间正在进行的动作.
如：He fell asleep when he was reading.他看书时睡着了.
2.用过去进行时表示现在主要是为了使语气委婉、客气.
如：I was wondering if you could give me a lift.我不知你能否让我搭一下车.
【注】一般过去时也有类似用法,但比较而言,用过去进行时显得更客气,更不肯定.
3.过去进行时表示感情色彩与现在进行时相似,过去进行时也可表示满意、称赞、惊讶、厌恶等感情色彩,也通常与 always,forever,continually等副词连用.
如：They were always quarrelling.他们老是吵架.
4.动词be的过去进行时
动词be的进行时也可表示过去一时的表现或暂时的状态.
比较：He was friendly.他很友好.(指过去长期如此)
He was being friendly.他当时显得很友好.(指当时一时的表现)
补充：when 的后面加一般过去时,而且动词是不延续性动词.　　while 的后面加过去进行时,动词是延续性动词.
特殊用法
1、当句子意思很清楚时,我们也可以把两个动词都换成一般过去时
We listened carefully while the teacher read the text.
老师读课文时,我们都仔细地听着.
2、表示按计划、安排过去将要发生的事.用于come,go,leave,start,arrive等表示位置转移的动词时,也可以用过去进行时表示过去将要发生的动作.
如：He told me that he was going soon.
他告诉我他很快就要走了.
3、表示故事发生的背景.
It was snowing as the medical team made its way to the front.
那支医疗小组往前线行进时,天正下着雪.
4、表示一个新的动作刚刚开始.
过去进行时可用来引出一个新的动作,这种用法颇有点儿像镜头转换.
Five minutes later,he stood in the doorway smoking a cigarette.
5分钟后,他已站在门口抽着烟.
5、过去进行时还可和when结构遥相呼应,含有意外之意.
I was walking in the street when someone called me.
我正在街上走时突然有人喊我.
6、用来陈述原因或用作借口.
She went to the doctor yesterday.She was having a lot of trouble with her heart.
她昨天去看病了.她患了很严重的心脏病.
7、与always,constantly等词连用,表示感情色彩.
The girl was always changing her mind.
这女孩老是改变主意.
常用的时间状语
　　this morning,the whole morning,all day ,yesterday,from nine to ten last evening,when,while ,at that time,.just now,a moment ago 　　My brother fell while he was riding his bicycle and hurt himself; 　　It was raining when they left the station;吗 　　When I got to the top of the mountain,the sun was shining.