The teaching building has five floors. My classroom is the third floor.A. onB. inC. atD.

问题补充：

The teaching building has five floors. My classroom is the third floor.

A. on

B. in

C. at

D. to

答案：

(答案→)A. on

B. in

C. at

D. to

解析：考查介词。句意“教学楼有五层，我的教室在第三层。”在第......层，用介词on。故选A。