Which site-to-site VPN solution allows Cisco routers, PIX Firewalls, and Cisco hardware clients to act as remote VPN clients in order to receive predefined security policies and configuration parameters from the VPN headend at the central site?（）
- A Easy VPN
- B GRE tunneling
- C Virtual Tunnel Interfaces
- D DynamicMultipoint VPN
- E Group Encrypted Transport VPN