请问May是用on还是in

请问May是用on还是in May 5th 前面是on 还是in 还是at? in May day?还是on May day? May 21st前用介词on还是in? May,1982 前面用介词in还是on 是on May 15th还是in May 15th啊 请问是on advance还是in advance 请问may I come in?下句用英语怎么回答.是yes please 还是yes you may It is in May 还是It is on May 英语中,节假日前是用什么介词呢?比如说在五一那一天,是in the May Day,还是on the May Day? 请问是in summer vacation还是on summer vacation? 请问及时的英语是in time 还是on time?