How is the Security Gateway VPN Domain created?

The following diagram illustrates how a VPN-1 Secure Client user tries to establish a VPN with hosts in the external_net and internal_net from the Internet.

How is the Security Gateway VPN Domain created?

A . Internal Gateway VPN Domain = internal_net;
External VPN Domain = external net + external gateway object + internal_net.
B . Internal Gateway VPN Domain = internal_net.
External Gateway VPN Domain = external_net + internal gateway object
C . Internal Gateway VPN Domain = internal_net;
External Gateway VPN Domain = internal_net + external_net
D . Internal Gateway VPN Domain = internal_net.
External Gateway VPN Domain = internal VPN Domain + internal gateway object + external_net

Answer: D