单项选择题 TestKing.com is configuring the serial interface of a Cisco router to connect to the router of a new ISP. A full T1 is being used for the Internet connection. After issuing the show interface serial 0/0 command, it is observed that the interface is UP and the line protocol is DOWN. Which of the following commands could fix this problem?（）

单项选择题 You have just installed a new web server on the Testking network. You are required to ensure that the web server is accessible from the Internet. The network uses private addressing, so an IP-to-registered address mapping is required.To do this, you enter the following command:TestKing(config)# ip nat inside source static 192.168.2.1 198.18.1.254 You unsuccessfully try to ping the Internet from a PC host on the LAN. During the troubleshooting process, you enter the "show ip nat translations" command but the output is blank. What is the most likely cause of the problem?（）

单项选择题 In order to troubleshoot an issue with the Testking frame relay network, you log into a remote router via a telnet session and issue the command "debug frame-relay lmi". After a long wait, you fail to see any output. What could be the cause of this problem?（）