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?（）

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?（）