《建筑设计防火规范》规定，当多层建筑物内设置自动扶梯、敞开楼梯等上下层相连通的开口时，其防火分区面积应按()计算。

A.上层面积

B.下层面积

C.上下层相连通的面积叠加

53. Our music teacher often enjoyed _____ playing the violin in his spare time.

A．him by

B．himself by

C．him in

D．himself with