while 常接进行时,它引导从句,主从句一般同事发生,所以主句一般也用进行时句子,可你的句子 While we were talking, the teacher was coming in. 中,come 是瞬间动词,一般不用进行时.而when 常接瞬间动词,引导从句,和主句动作不一定同时发生,可有先有后（when先,主句后）,所以这个We were talking when the teacher came in. 综前所述,是对的!
while 常接进行时,它引导从句,主从句一般同事发生,所以主句一般也用进行时句子,可你的句子 While we were talking, the teacher was coming in. 中,come 是瞬间动词,一般不用进行时.而when 常接瞬间动词,引导从句,和主句动作不一定同时发生,可有先有后（when先,主句后）,所以这个We were talking when the teacher came in. 综前所述,是对的!