区别几个与'time"有关的词组

问题描述:

区别几个与'time"有关的词组
at certain time
at certain times
at a certain time
这些词组都对的吗?有什么区别呢?

在某一时刻 at certain time 在特定的时间 at certain times在某个时间at a certain time 例句:Payment at a certain time after sight.见票后若干日付款.例句:Animals can be conditioned to expect food at cert...