是on a party,还是in a party,at a party 为什么?

是on a party,还是in a party,at a party 为什么? 是“in”a welcome party还是“at”a welcome party? 是in the party 还是 on the party in the day 还是on the day 题目是这样的 We have a party（）the day. put on a party on a costume party 还是at a costume party到底用什么啊我凌乱了 a costume party 前加on还是at 是on a cold morning 还是in a cold morning? 是on a fine morning还是in a fine morning? 是in a windy day还是on a windy day? 是sit in a chair还是sit on a chair? 是on a field trip,还是 in a field trip 是in a snoWY day还是on a snoWY day 是on a week 还是in a week 是on a lake 还是in a lake? 乘电梯是on a lift还是in a lift 是sitting in a boat 还是sitting on a boat? 是sleep in a bed还是sleep on a bed?