用法一：when和while的区别
when后面接短动作或长动作，while后面只能接长动作。短动作用一般过去时，长动作用过去进行时。
I was walking past the car when it exploded.
The car exploded when I was walking.
The car exploded while I was walking.
*注：都是长动作那就都用过去进行时
While I was studying last night,my wife was watching TV.我昨晚学习的时候，我妻子在看电视。
用法二：描述一个过去特定时刻正在发生的事情
I was discussing my thesis with my director at this time last night.我昨晚的这个时候正在和我导师讨论论文。
用法三：表示委婉的请求或提建议
I was wondering if you'd like to lend me your car.你能把车借我吗？
I was wondering if you could lend me your car.你能把车借我吗？
