为什么是 on Monday afternoon ，而不是 in Monday afternoon

在指特定的某一天的下午时要用On,没有指明是哪一天用In
on
Monday
afternoon,
而用
in
the
afternoon

扩展阅读：on the sunday morning ... 女生发move on暗示什么 ... on next monday ... on monday是什么意思 ... on monday we raise ... come on the way abc ... in monday afternoon ... on mondays和on monday区别 ... you and me jennie ...