You deploy mobile devices that run Microsoft Windows Mobile 5.0.   A Microsoft Windows Server 2003 server that runs Routing and Remote Access is configured to allow virtual private network （VPN） connections that are as secure as possible.   You need to connect the Windows Mobilebased devices to the VPN server. You also need to ensure that both ends of the VPN tunnel are authenticated.  Which two actions should you perform？（）

• A、Select L2TP/IPSec on each Windows Mobilebased device.
• B、Obtain and install a certificate on each Windows Mobilebased device.
• C、Configure the appropriate pre-shared key on each Windows Mobilebased device.
• D、Select Point-to-Point Tunneling Protocol （PPTP） on each Windows Mobilebased device.