What is not a difference between VPN tunnel authentication and per-user authentication?（）

• A、VPN tunnel authentication is part of the IKE specification. 
• B、VPN tunnel authentication does not control which end user can use the IPSec SA (VPN tunnel).
• C、User authentication is used to control access for a specific user ID, and can be used with or without a VPN tunnel for network access authorization. 
• D、802.1X with EAP-TLS (X.509 certificates) can be used to authenticate an IPSec tunnel.