为什么是on a cold night,in a sunny morning

为什么是on a cold night,in a sunny morning 是on a cold morning 还是in a cold morning? 用in a sunny morning 还是on a sunny morning?为什么?那on Sunday morn on a sunny morning 还是in a sunny morning on a sunny morning为什么用on? in a cold morning还是on a cold morning? 请问是In a cold winter morning 还是 on a cold winter morning? ( ) a cold winter night.是用in还是on? 谁能解释为什么用in a sunny morning 用in.on Monday morning 用on.和in、on、 是on a cold winter morning还是in? _______a cold morning A.IN B.on in a very cold morning 还是用on a very cold morning,到底是用in 还是on