若放置带铜V型宫内节育器，此类宫内节育器的作用为
A．降低脱落率B．防止嵌顿C．减少出血D．防止感染E．增强避孕效果
参考答案：E
– When did you ________ to do the work?
- Two months ago, we are through 80% of it at the moment.
A．set off
B．set out
C．set up
D．set about
在图7-12所示的OSPF协议多区域结构中，路由器___63___为主干路由器；___64___为区域边界路由器。
64（）
A．R2、R3、R8
B．R1、R4、R7
C．R1、R2、R3、R5、R8
D．R3、R7、R8
