Miss Green goes to the doctor's ( on ) Monday mornings.

问题描述:

Miss Green goes to the doctor's ( on ) Monday mornings.
括号内填的不是In吗?为什么是on,

in用在“早晨/上午、下午、晚上\”名词前,如: in the morning,in the afternoon,in the evening 如果表示某一天的上午、下午和晚上,要用介词on.如:on Sunday morning,on Saturday evening