18．—Jim, are you ______ this Saturday?

—Oh, sorry. I need to go to the bookshop _____ the bank on Saturday.

A．convenient; and

B．convenient; as well as

C．available; as well as

D．available; with

【问题4】
若采用电视铜缆接入计算机主干网络，用户端需增添什么设备网络通信速率为多少