on a hot summer afternoon 为什么用on

on a hot afternoon对吗?为什么不是in而是on? What a fun it is to go swimming on a hot summer afternoon 这句 a hot summer day 前面用in还是on on a warm evening of summer为什么用on? on the summer evening为什么用on on hot summer days的意思 a hot summer day 前面用on 还是in ,问什么?顺便说一句,我郁闷了好久的 On a hot summer holiday,a little boy decided to go for a swi Her brother was born () a hot summer afternoon. .Some years ago on a hot summer day in south Florida a littl Playing in the water lots of fun on a hot summer day.(A)is ( _____ it is to jump into a river on a hot summer day!