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? on a costume party 还是at a costume party at a party 意思是 at a party翻译 put on a party a costume party 前加on还是at 为什么是a surprise party而不是a surprising party? join the party ;join in a party 究竟是attend a party还是take part in a party? at the party还是in the party? 是in the party 还是 on the party