Early ( ) the morning of May 1,we started off for the mountain vi_英语解答

Early ( ) the morning of May 1,we started off for the mountain village.应该填ON 还是IN,
说明下理由,

人气：213 ℃　时间：2020-01-24 21:00:14

解答

用on.
单独说在早上是in the morning.
但是具体某一天的上午、下午、晚上,用on