这里为什么用intheevening,不用ontheevening,不是具体某一天的晚上吗WuYifanwasbusylastweekend.HevisitedhisgrandmotherSaturdaymorning.Itwashisgrandmother’sbirthday.Theycookednoodlestogether.In（我说的就是这

Question

这里为什么用in the evening,不用on the evening,不是具体某一天的晚上吗
Wu Yifan was busy last weekend.He visited his grandmother Saturday morning.It was his grandmother’s birthday.They cooked noodles together.In（我说的就是这个in,明明是具体某一天的晚上,也就是周六的晚上） the evening,they watched TV.（这里也是,明明是具体某一天的早上,就是周日的早上,为什么不用on） Sunday morning,Wu Yifan played football with his friends.In(这里也一样,为什么不用on?) the afternoon,he washed his clothes and cleaned his room.

Answer 1

in the evening,这是一个固定短语,且这个短语中并没有提周六周天,前面提了,和这个句子没关系,如果是on the saturday morning
,这种短语中就具体到某一天的,才用on.