（1）表示过去某一时刻或阶段正在发生的动作。
►. I was playing chess at 8 yesterday evening.
►. When I arrived, they were watching TV.
►. They were doing housework this time last week.
（2）用于条件状语从句中表示过去将来进行的动作。
►. She told me to wake him up if she was sleeping.
►. I asked my friend to warn me about it as long as I was driving too fast.
测试精编
1. My brother ________ while he ________ his bicycle and hurt himself.
A. fell / was riding B. feel / were riding
C. had fallen / rode D. had fallen / was riding
2. He ________ his leg as he ________ in a football match.
A. broke / played B. was breaking / was playing
C. broke / was playing D. was breaking / played
3. -My father will be here tomorrow. -I thought that he ________ today.
A. was corning B. is coming
C. will come D. comes
4. Jack was going out of the shop when he collided with an old woman who ________ in.
A. come B. was coming C. had been coming D. had come
5. Michike couldn't come to the telephone when Mr. Smith called her because she ________ in the lab.
A. had been working B. has been working
C. was working D. worked
KEYS
1. A 2. C 3. A 4. B 5. C
