He’s _______as a “bellyacher” —he’s always complaining about something.

A．who is known

B．whom is known

C．what is known

D．which is known

地理信息系统在应急联动系统中的主要作用是（）.

A.统一呼叫号码

B.统一指挥

C.提供数据存储

D.显示出救助事件地点附近的公安、交警、消防、急救等部门警力和救助资源的分布