the summer 前加on还是in还是at

the summer 前加on还是in还是at 是at the summer 还是 in the summer 还是on the summer 在具体时间前加on还是in还是at? 词组,是ceremony前加at还是in ,on? trip前加什么介词是in on 还是 at Christmas Eve前加in at to还是on December 2014前加什么介词,in,on还是at? the and of October前加at,in,of还是on at summer 还是IN SUMMER the morning of sunday前用on还是at in ( ) the summer holiday 填in还是on 在暑假是on summer还是in summer还是at summer