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请根据如图所示的网络结构回答下列问题。

某网络结构示意图

请填写表1中路由器RG的路由表项①～⑤

答案

参考答案：

①63.0/28

②172.16.63.16/28或172.16.56.0/22

③172.16.63.241

④172.16.56.0/22或172.16.63.16/28，但需与②不同

⑤S1

解析：

在如图所示的连接路由器的接口中，标有S0 (Serial 0)、S1(Setral 1)的是串行线路标记，E0、E1、E2表示Ethernet接口。其中，路由器RG通过两条专线S0、S1分别与路由器RE、RF连接；路由器RE通过两个Ethernet接口分别与路由器RA、RB连接；路由器RF通过两个Ethernet接口分别与路由器RC、RD连接。RA、RB、RC、RD分别连接了172.16.0.0/24～172.16.3.0/24、156.26v56.0/24～172.16.59.0/24等8个子网。由于在如图所示的网络中共有12个子网，因此路由器RG的路由表可能会有12个条目，如表2所示。

观察表2可知，路由器RG的路由表可以简化。其中，前4项可以保留，后8项可以考虑合并成两项。按照“最长前缀匹配”的原则，可以寻找到相同输出接口(S0)的172.16.0.0/24～172.16.3.0/24等4项的最长相同的前缀。分别将这4条路由地址中第3个字节数字转化为二进制数，即0=(0000 0000)2，1=(0000 0001)2，2=(0000 0010)2，3=(0000 0011)2。这些数字只有前6位二进制数(划线部分)相同，因此路由汇聚后的IP地址的第3个字节数字的二进制表示是：0000 0000，即这4条路由进行路由汇聚后的IP地址为：172.16.0.0/22。 同理，可以寻找到相同输出接口(S1)的172.16.56.0/24～172.16.59.0/24．等4项的最长相同的前缀。分别将这4条路由地址中第3个字节数字转化为二进制数，即56=(0011 1000)2，57=(0011 1001)2，58=(0011 1010)2，59=(0011 1011)2。这些数字只有前6位二进制数(阴影部分)相同，因此这4条路由进行路由汇聚后的IP地址为：172.16.56.0/22。 综上分析，经CIDR路由汇聚后的核心路由器RG路由表如表3所示，路由条目数由12条减少到6条。

单项选择题

星形细胞瘤据其组成的细胞类型可分四型，不属于其类型为（）

A.纤维细胞型

B.毛发细胞型

C.原浆细胞型

D.肥胖细胞型

E.生殖细胞型
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单项选择题

The common cold is the world’s most widespread illness, which is plagues that flesh receives.
The most widespread mistake of all is that colds are caused by cold. They are not. They are caused by viruses passing on from person to person. You catch a cold by coming into contact, directly or indirectly, with someone who already has one. If cold causes colds, it would be reasonable to expect the Eskimos to suffer from them forever. But they do not. And in isolated Arctic regions explorers have reported being free from colds until coming into contact again with infected people from the outside world by way of packages and mail dropped from airplanes.
During the First World War soldiers who spent long periods in the trenches, cold and wet, showed no increased tendency to catch colds.
In the Second World War prisoners at the notorious Auschwitz concentration camp, naked and starving, were astonished to find that they seldom had colds.
At the Common Cold Research Unit in England, volunteers took part in Experiments in which they gave themselves to the discomforts of being cold and wet for long stretches of time. After taking hot baths, they put on bathing suits, allowed themselves to be with cold water, and then stood about dripping wet in drafty room. Some wore wet socks all day while others exercised in the rain until close to exhaustion. Not one of the volunteers came down with a cold unless a cold virus was actually dropped in his nose.
If, then, cold and wet have nothing to do with catching colds, why are they more frequent in the winter Despite the most pains—taking research, no one has yet found the answer. One explanation offered by scientists is that people tend to stay together indoors more in cold weather than at other times, and this makes it easier for cold viruses to be passed on.
No one has yet found a cure for the cold. There are drugs and pain suppressors such as aspirin, but all they do is to relieve the symptoms.

Arctic explorers may catch colds when ______.

A. they are working in the isolated Arctic regions
B. they are writing reports in terribly cold weather
C. they are free from work in the isolated Arctic regions
D. they are coming into touch again with the outside world
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