— It's said a pianist will perform at Poly Theater on Friday evening. Is it Lang Lang?

— Yes, it _______ him. He _______ for a week.

A．must be; has arrived here

B．Can’t; has been here

C．must be; has been here

D．maybe; has arrived here

下列关于宽带城域网汇聚层基本功能的描述中，错误的是（）。

A．汇接接入层的用户流量，进行数据转发和交换

B．根据接入层的用户流量，进行流量均衡、安全控制等处理

C．提供用户访问Internet所需要的路由服务

D．根据处理结果把用户流量转发到核心交换层