虚拟化技术在容灾系统中的应用可以带来哪些好处（）

A.用户掌握系统建设主动权

B.提高应用系统性能

C.增加硬件投入降低软件投入

D.降低总体拥有成本

You’d better choose someone 　　you think　　　 kind and friendly to help you.

A．whom; to be

B．who; is

C．that; is

D．which; to be