You can only be sure of ____ you have at present; you cannot be sure of something ____ you might get

in the future. [ ]

A. that; what

B. what; /

C. which; that

D. /; that

多路复用的主要目的不包括（ ）。

A．提高通信线路利用率

B．提高通信线路通信能力

C．提高通信线路数据率

D．降低通信线路通信费用