题目：
A multicast router may receive thousands of multicast (6) every day for different groups. If a router has no knowledge about the membership status of the (7) , it must broadcast all of these packets. This creates a lot of traffic and consumes (8) . A better solution is to keep a list of groups in the network for which there is at least one loyal member. (9) helps the multicast router create and update this list. For each group, there is one router that has the duty of distributing the (10) packets destined for that group. This means that if there are three multicast routers connected to a network, their lists of groupids are mutually exclusive. A host or multicast router can have membership in a group.
A．anycast
B．multicast
C．unicast
D．broadcast
答案：
参考答案：B
解析：[参考译文] 组播路由器每天可能接收到成千上万个组播分组。如果路由器不了解组播成员的主机状态，它就必须广播所有的分组。这样就产生了大量的通信，耗费了很多带宽。一个比较好的解决方案是在网络中维护一个组成员表，每个组中至少有一个忠实的成员。IGMP协议帮助组播路由器生成和更新这个表。对于每一组，要有一个路由器负责发布该组的组播分组。这意味着如果有3个组播路由器连接在一个网络中，那么它们的组标识符列表就是相互不包含的。一个主机或组播路由器可以成为多个组的成员。
