根据句子意思，填入合适的介词。

小题1:You should listen __________ the teacher in class.

小题2:Are you ready __________ the class?

小题3:There are two beautiful pictures __________ the wall.

小题4:Happy Birthday! This is the present _________ you.

小题5:We are having a sports meeting __________ the playground now.

非检修的设备，其带电部分在工作人员的（）位置，且无可靠安全措施，其设备必须停电。

A.正面

B.两侧

C.上下

D.后面