1.on表示在具体某一天及具体某一天的上午、下午和晚上.例:on the morning of July 2,on Sunday afternoon,on a cold winter evening .2.当 morning.afternoon.evening有前位定语或后置定语限定时.就不用in而用on..例:on a hot (summer) noon,on Monday morning,on the morning of March
in常用于在...里,在...上
强调一段时间