on or in fine mornings 是on 还是 in

on or in fine mornings 是on 还是 in 是in Sunday mornings还是on Sunday mornings 是on a fine morning还是in a fine morning? () the weekend in or on? on or in christmas day on april or in april? a report (on) or (in) newspapers此句中是用on还是in? 那星期用什么,On还是In or at 是IN THE PLAYGROUND 还是ON? 到底是on holiday还是in holiday 请问是on advance还是in advance 是in theday还是on the day