You configure a new SQL Server 2005 computer to use TCP/IP with all default settings. Your corporate policy requires that each server use a firewall. You find that you can connect to the SQL Server instance from the local computer. However, client computers cannot connect to the SQL Server instance. You need to identify the most likely cause of the connection issues. What should you do first?（）

• A、Ensure that port 1433 is open in your firewall. 
• B、Ensure that port 443 is open in your firewall. 
• C、Ensure that client computers connect by using Shared Memory protocol. 
• D、Ensure that the server is not paused.