四台Linux主机通过图1所示的方式互联起来，则实现PCI与PC4之间互访的步骤为：

 1．运行(46 命令关闭计算机，在PC2与PC3上添加第二块网卡(ethl)，重新启动；

 2．在PC2与PC3上为第二块网卡分配IP地址，并激活该网络接口，对于PC3，应执行(47)；

 3．如果使用routed作为路由器进程，则作为路由器的PC2与PC3仅支持路由协议(48)；如果在PC2与PC3上设置静态路由信息并开启路由功能，对于PC2则应执行(49)；

 4．在PC1和PC4上配置各自的默认网关，对于PCI，应执行(50)。

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Ipv6 is(71)for "Internet Protocol Version 6"。Ipv6 is the "next generation" protocol design by the IETF to(72)the current version Inernet Protocol, IP Version 4. Most of today's internet uses Ipv4, which is now nearly twenty years old. Ipv4 has been remarkably resilient in spite of its age, but it is beginging to have problems. Most importantly, there is a growing(73)of Ipv4 addresses, which are needed by all new machines added to the Internet. Ipv6 fixs a number of problems in Ipv4, shch as the(74)number of available Ipv4 addresses. It also adds many improvements to Ipv4 in areas such as souting and network autoconfiguration. Ipv6 is expected to gradually replace Ipv4, with the two coexing for a number of years during a transition(75)A.

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In the following essay, each blank has four choices. Choose the most suitable one from the four choices and write down in the answer sheet.

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