Your company uses Remote Desktop Services （RDS）. You install and configure the Remote Desktop Gateway （RD Gateway） role service on a server that runs Windows Server 2008 R2. Employees connect to RDS from unmanaged remote computers. Employees are unable to access the RD Gateway server from the unmanaged remote computers.You need to ensure that employees can access the RD Gateway server. What should you do？（）

• A、Create a Remote Desktop resource authorization policy （RD RAP）.
• B、Create a Remote Desktop connection authorization policy （RD CAP）.
• C、On the RD Gateway server， open port 3389 on the Windows Firewall.
• D、On the RD Gateway server， configure Network Access Protection （NAP） health policy checking.