1.月份,年份前用介词in:
In January,2005 / 2005年元月
2.几点钟前用介词at
at two /在两点
at 7p.m/在下午七点
3.it lasts ( for) three hours.
for表持续时间
这次会议已经持续了两小时了.
The meeting has lasted for two hours.
4.表具体某一天或星期几,用介词on.
从那时起,新年就在一月一日.
From then on,New Year's Day was on January 1
on Monday,在周一.