:
My brother fell while he was riding his bicycle and hurt himself. 我兄弟骑车时摔了下来，受了伤。
It was raining when they left the station. 他们离开车站时，正下着雨。
When I got to the top of the mountain, the sun was shining. 我到达山顶时，阳光灿烂。
典型例题
1） Mary ___ a dress when she cut her finger.
A. made B. is making C. was making D. makes
答案C.
割伤手指是已发生的事情，应用过去时。同时，when表时间的同时性，"玛丽在做衣服时"提供事情发生的背景，因此用过去进行时。
2） As she ___ the newspaper, Granny ___ asleep.
A. read；was falling B. was reading； fell C. was reading； was falling D. read；fell
答案B.句中的as = when, while，意为"当……之时"。描述一件事发生的背景时，用过去进行；一个长动作发生的时候，另一个短动作发生。句意为 "在她看报纸时，奶奶睡着了。"句中的 fell（fall的过去时），是系动词，后跟形容词，如：fall sick
