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 RADIU
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.