You are the administrator of a Windows 2000 Professional computer， which has a 56 Kbps modem， connected to itself. You want the users on your company’s network to be able to connect to the Internet using your computer. But， you do not want to allow any other operations than HTTP and FTP. Which ports will you allow through this connection？ （）

A. Port 80
B. Port 21
C. Port 25
D. Port 81