介绍:
一、was/were doing
过去进行时在:过去某个特定的时间正在进行或发生的动作
He is writing now.（at this time yesterday）
He was writing at this time yesterday.
练习：1. She is sweeping the floor now. (then)
2. I am preparing for the trip. (at7:00 this morning)
3. Peter, what are you doing there? (just now) 二、时间状语从句:
表示当…时,… 通常由when, while, as引导
例：当他在写的时候，她在哭。
While he was /is writing，she was/is crying.
三、时态：可以是现在时，也可以是过去时，但是主从句的时态必须保持一致。
我回家时， 妻子在做饭。
When I come home, my wife is cooking.
When I came home my wife was
cooking.
四、动词： 延续性动词使用现在/过去进行时，非延续性动词用一般现在/过去时。
He cut himself while he was shaving.
五、连词
when：时态灵活，由动词决定
while：其后必须是进行时
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