单选题 You configure your Windows 2000 Professional computer for Internet Connection Sharing and for TCP/IP filtering as shown in the exhibit.

A、 Add Port 21 to the TCP Ports section.
B、 Add Port 138 to the TCP Ports section.
C、 Add Port 21 to the IP Ports section.
D、 Add Port 138 to the IP Ports section.

【正确答案】 A

【答案解析】解析：Explanation: The FTP protocol uses the TCP port 21. In the exhibit the UDP port 21 has been incorrectly added instead of the TCP port. Incorrect answers: B: The FTP protocol uses Port 21 not Port 138. C: The port 21 should be added as a TCP port 21, not as a UDP port or as an IP protocol. IP is also a network protocol and not a port. D: The FTP protocol uses TCP port 21 not port 138. IP is also a network protocol and not a port.