Ray is a new graduate, and it seems that he has difficulty in dealing with ________ problems arise.

A．whichever

B．whenever

C．whatever

D．wherever

接入网提供开放的（），兼容任何种类的交换设备，可独立于交换设备进行升级，并能很方便地引入新业务，也易于向宽带网过渡。

A.Z接口

B.U接口

C.V5接口

D.SNI接口