英语句子日期、月份和星期前面各应该加in还是on？

Question

如题。可以的话，帮我填下面的题目，填in或者on。
His birthday is ( ) May 21th.
It is always cold ( )February.
He is going to arrive ( ) Monday.

Answer 1

on
in
on
月份前用in,年份前用in, 只有具体到某一天时用on,所以星期几具体到一天用on

Answer 2

on
in
on

Answer 3

on in on

Answer 4

on
in
in