为什么是in the early morning却是on a dark night?

为什么是in the early morning却是on a dark night? 为什么是on a cold night,in a sunny morning 为什么是in the early morning 为什么是in the early morning,有修饰的早中晚不是用on吗 in a dark rainy night还是on a dark rainy night 为什么 in the early morning 还是 on the early morning early morning on new year's day和one night in the winter,这两句话 early in the morning是对的 哪early in the morning of 1st The story took place -------a dark night.A at B in C on Dfro 找一首英文歌,第一句是Early in the morning On a snowy night为什么是on in the early morning?