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,半小时后回来.
on
(表示时间)在…之时
It occurred on the morning of the fifteenth.
事情发生在15号的上午.
On arriving home,I was met by my daughter.
到家时我的女儿出来迎接我.
at
(表示时间)在,在…时刻[时辰,期间,阶段,时节]; 在…岁时
The meeting will open at 15 ∶ 00.
会议在下午三点钟开始.
during
1、(表示时间)在某情况的一段时间
Where shall you go during the summer?
今年夏天你将到什么地方去?
2、(表示时间)在…期间,当…之时,在…期间的某个时候
The fire started during the workmen's dinner.
火灾是在工人们吃饭时发生的.
