The Yangtze River is almost          the Pearl River.

A．twice longer than

B．longer twice than

C．twice length of

D．as twice long as

关于精馏塔上N2管线作用，下列说法正确的是（）。

A、当事故停车或正常停车时保压用

B、装置开车时置换用

C、正常运转时维持塔压为正压以防因冷凝温度过低使塔顶形成负压

D、装置着火时作消防灭火用