高中英语as while区别

题目

高中英语as while区别
I saw her just ______ she was getting off the train.
A.as B.while
为什么选A

答案

while表示的时间是一段,而不是一个时间点,如：While he was eating his breakfast,he heard the doorbell ring.(强调吃饭的过程）
as强调“同一时间”,或“一前一后”发生的事,
she was getting off the train就是强调她下火车的那一个时间点,而不是一段时间