帧中继采用水平分割是为了________。
A．增加路由器更新
B．防止路由选择回路
C．缩短收敛时间
D．帧中继不使用水平分割
参考答案：D
小威家院子里长着一棵老槐树．花开时节，满院飘香．请用微粒的观点解释这一现象：______．
When John woke up he was in the hospital, but he didn’t know how that had .
A．been happened
B．come about
C．been come about
D．been taken place
