Which three statements about the Cisco Easy VPN feature are true？（）

• A、If the VPN server is configured for Xauth， the VPN client waits for a username / password challenge.
• B、The Cisco Easy VPN feature only supports transform sets that provide authentication and encryption.
• C、The VPN client initiates aggressive mode （AM） if a pre-shared key is used for authentication during the IKE phase 1 process.
• D、The VPN client verifies a server username/password challenge by using a AAA authentication server that supports TACACS+ or RADIUS.
• E、The VPN server can only be enabled on Cisco PIX Firewalls and Cisco VPN 3000 series concentrators.
• F、When connecting with a VPN client，the VPN server must be configured for ISAKMP group 1，2 or 5.