at one time和at a time的区别是什么?

A.at a time 依次,逐一,每次.如;1.Don't try to do everything at once,take it a bit at a time.不要什么事情都一块干,要一次做一点.2.Take the pills two at a time.每次服2粒.B.at one time一度,从前.如:At one t...