Everybody went to the party, but Li Hong stayed at home _____ her mother was sick.

A．when

B．because

C．although

D．unless

总线制火灾应急广播系统由消防控制室的广播设备，配合火灾报警控制器、()及现场放音设备组成。

A、消防广播分配盘 

B、扬声器 

C、广播功率放大器 

D、广播切换模块