my brother was born ( ) the morning of January 1 用in还是on?

问题描述:

my brother was born ( ) the morning of January 1 用in还是on?

on the morning of 具体日期...
有具体日期的时候介词用on
没有具体日期的话用 in
在早上 in the morning
在傍晚 in the evening of Monday.星期一的傍晚 (非具体哪一天)
:)