1.in+月份、季节,in+the(定冠词) +morning/afternoon/evening.
如：in May in summer
2.on+几月几日、星期几、节日、哪一天的上/中/下午.
如：on May 1st on Monday on New Year's Day
on Sunday morning
★on the morning of+几月几日.如：on the morning of May 1st
★on the+adj(形容词)+上/中/下午.如：on the sunny morning
3.at+时间点 、noon/night.
如：at 7:00 at noon at night
▲答案：in the morning on Sunday on Sunday morning