in、on、at、during的用法in、on、at、during这几个词都是时间介词,到底它们有虾米区别呢?

in(表示时间)在…时期,在…之后,In her twenties and thirties she had had no difficulty getting jobs.她在二三十岁时找工作一点也不困难.I cannot see you now,come back in half an hour.我现在不能见你,半小时...