过去进行时
过去进行时： I was walking down the street when it began to rain.
When it began to rain
now
I was walking
I was walking down the street when it began to rain. I was not walking down the street when it began to rain. Were you walking down the street when it began to rain?
据说，她去年写0 了一本小说。
3. 常用于介绍故事的背景。 （一）
Once an Jack was traveling in the desert. （二）描述一件事发生的背景；一个长动作发生
的时候，另一个短动作发生（长动作用过去进行 时，短动作用一般过去时）。也可以表示两个动
作同时发生，此时均用过去进行时
• a. The children were playing when they heard the sound of a motor bike.
• b. He is strong while his brother is weak.
• 5.通常不能用于过去进行时的动词主要有： agree, be, believe, belong, care, forget, hate, have(拥有), hear, know, like, love, mean, mind, notice, own, remember, seem, suppose, understand, want, wish等。例如：
4. When/ While“当……的时候”的区别
