Question

the young lady was walking in the street when she hear a voice from behind why when or while

Answer 1

原题中有个词打错，先纠正再分析——
The young lady was walking in the street when she【 heared 】a voice from behind .why when or while
句意：这位女士当时正在街道上散步，突然她听到身后传来一个声音。
这里，用when，表达【突然，就在那时】。
构成固定句型结构 ：be doing sth...when
意义上相当于：
The young lady was walking in the street 【and suddenly】 she【 heared 】a voice from behind .
使用when 的类似固定句型还有：
be to do sth when
be about to do sth when
be at the point of doing sth when
hardly/scarcely when
祝你开心如意！O(∩_∩)O~~

Answer 2

when对，而且后面的hear要改为heard
其实就是一个固定搭配，was/were doing ...when ...表示“正在做某事……突然……”
这句话的意思就是“那个年轻的妇女正在街上走，突然她听到身后传来一个声音”
类似用when的还有be about to do ...when ...正打算做某事……突然……

Answer 3

when对，因为前半句（the young lady was walking in the street ）是过去进行时，那后半句就应是一般过去时，而且when引导一般过去式，故when对。（不过，hear要改为过去式heard。）