It was ______it rained hard ______ the football match had to be put off till next week? 

A．because of, which

B．why, that

C．why, which

D．because, that

程控交换机的硬件系统主要包括七部分：用户线接口电路、中继线接口电路、非话音业务接口设备、（）、信号设备、处理机和外围设备。