on/in freezing day People often wear gloves and hats to keep themselves warm (in/on) freezing day.为什么呢?

on/in freezing day People often wear gloves and hats to keep themselves warm (in/on) freezing day.
为什么呢?

第一个用on,关于,第二个用in.在.的日子

到底是问我哪一个好还是为什么两个都可以啊？

on
为什么会有两个啊