There were many signal systems in Chinese railways, which seriously affected the transportation efficiency. There was an urgent need to set unified technical standards for _______. 中国铁路信号系统较多，严重影响了运输效率。迫切需要为_______制定统一的技术标准。
A、communication system 通信系统
B、railway signal system铁路信号系统
C、power supply system 供电系统