.表是什么时间什么年龄用at
2.表示“在上、下午”,“在晚上、傍晚”用in,如要表示“某日上午”早些时候或晚些时候也用in,表示什么月、什么季度、什么年份、什么世纪要用in
3.但是若在morning等词前有修饰语时（如cold、fine等）用on
在某日的早晨也用on
题目：
1）She got married _ 22.
2) We left Hangzhou _ the afternoon of October 15.
3) He called me _ Sunday morning.
4) He phoned me _ the early morning of June 4.
5) They arrived _ the late afternoon of 20th December.
6) My daughter was born _ July 1961.
7) The First World War broke out _ 1941 and ended _ 1918.
8) I shall take a holiday _ summer.
key:1)at 2)on 3)on 4)in 5)in 6)in 7)in in 8)in