I am quite busy weekends I have to go to English class Sunday mornings and dancing class a

问题补充：

I am quite busy weekends I have to go to English class Sunday mornings and dancing class after lunch.

A. at; in

B. in; in

C. in; on

D. on; on

答案：

A. at; in

B. in; in

C. in; on

(答案→)D. on; on

解析：表示在周末可用介词on或者at，表示在星期几只能用on，故本题选D。