夏天，小明发现家中常用点燃蚊香来驱蚊，而在人离开后蚊香仍然燃烧而造成浪费，于是他想能不能测出蚊香燃烧的速度，根据大致的时间开确定每次使用蚊香的长度，从而达到节约的目的，请你帮他设计一个实验来测定蚊香燃烧的速度．

a．实验器材：火柴、蚊香、______、______、______

b．简述主要操作过程，写出所要测量的量或要记录的物理量（用字母表示）

c．蚊香燃烧的平均速度计算公式______（用字母表示）

A multicast router may receive thousands of multicast （） every day for different groups. If a router has no knowledge about the membership status of the （） , it must broadcast all of these packets. This creates a lot of traffic and consumes （）. A better solution is to keep a list of groups in the network for which there is at least one loyal member. （） helps the multicast router create and update this list. For each group, there is one router that has the duty of distributing the （） 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.

For each group, there is one router that has the duty of distributing the （） packets destined for that group.

A. anycast

B. multicast

C. unicast

D. broadcast