______ is known to all, Great Britain and Northern Ireland ______the United Kingdom 

A．It; are consisted of

B．As; are made up of

C．It; consist of

D．As; make up

生成树协议可以把交换机端口置于五种状态机，下列关于阻塞状态说法正确的是（）

A.数据转发被阻塞，进行地址学习

B.数据转发被阻塞，监听BPDU

C.数据转发被阻塞，不监听BPDU

D.进行数据转发，进行地址学习