"On the first morning"为什么前面要用"on"?请分析.

on the first of Was the traffic_____(heavy)this mornin on the first floor是什么意思 on April first 和 on April the first 那个对 on first day 对还是 on the first day 对 at the first floor还是on the first floor 有没有in the first day,on the first day on the first day还是in the first day is on the first day of the first lunar month 速求 on the first day of the first the canteen is on the first Is your classroom on（）floor?one first the first ON the morning of March first.可以这样翻译吗?on the morning on march first the first turn on the right 还是take the first turnning on the right on the first day还是in the first day还是at the first? on the first 只要这个回答 May Day is on the first _____May. Lafee 《on the first night》歌词