1、at的用法：通常用在时刻钟点，夜晚中午上午或者某些固定短语中
2、例如：at six o’clock
at noon
at night
at the beginning of
at the end of
at the age of
3、in的用法：通常用在年月，季节，白天晚上等词前。
4、例如：in 2017
in May,2017
in the morning
in the afternoon
in the evening
in the daytime
in spring
in summer
5、on的用法：通常用在星期，节日具体的某一天。
6、例如:
on Monday
on Monday morning
on March 1st,2017
on the afternoon of May 2nd
on Teachers’ Day
on a windy evening(前有修饰词,具体到刮风的那天晚上,属于具体某一天用on)
on a cold night
