在暑假是on summer还是in summer还是at summer

在暑假是on summer还是in summer还是at summer at summer 还是IN SUMMER 是in summer还是on summer 是at the summer 还是 in the summer 还是on the summer 在夏天是用in summer 还是on summer 请问是in summer vacation还是on summer vacation? 是on summer holidays还是in summer holidays? 是in summer 还是in the summer the summer 前加on还是in还是at in a summer night还是at a summer night 是in summer vacation还是in the summer vacation啊? ( ) the summer holiday 填in还是on