In an L2TP voluntary tunneling scenario， the VPDN tunnel is terminated between：（）

A. PFS group.
B. Encryption algorithm.
C. Hashing Algorithm.
D. Authenticationmethod.
E. Lifetime duration.

A. The sender of the message.
B. The receipient of the message.
C. The sender’s administrator who provides the sender with the PGP program.
D. A third party that belongs to what’s often known as "web of trust"， that can verify the relationship between the user and the key.
E. The vendor of the PGP program.