A man went to a farm．While he was there，he saw a pig with a wooden leg．This surprised him so much．He decided to ask the farmer about it．

“This isn’t a common pig and l am very lucky to have him．”said the farmer．“Only two days ago there was a fire in chicken shed(鸡舍)when 1 was away from the farm．The pig noticed this and immediately let all the chickens out into the yard．He then phoned the firemen(消防员)and asked them for help．”

“AIso．a few weeks ago，when I was driving my truck down a steep hill，the truck hit a tree and 1 was badly hurt．The pig rushed to the truck and pulled me out of just before the truck caught fire．”

When the farmer was just about to tell another story，the man said，“Yes, yes，but what about the wooden leg?”

“Well．”said the farmer，“when you’ve got a pig as good as that，you don’t eat it all at once”

小题1:The pig lost a leg while he was trying to save the farmer’s chickens.

多协议标记交换（MPLS）是IETF 提出的第三层交换标准，下面有关MPLS 的描述中，正确的是（ ） 。

A．MPLS 支持各种网络层协议，带有MPLS 标记的分组必须封装在PPP 帧中传送

B．MPLS 标记在各个子网中是特定分组的唯一标识

C．路由器可以根据转发目标把多个IP 流聚合在一起，组成一个转发等价类（FEC）

D．传送带有MPLS 标记的分组之前先要建立对应的网络连接