The Network Administrator Configures a VPN Tunnel from a Remote

The network administrator configures a VPN tunnel from a remote office to the main facility.A problem has occurred in the link.Which are the main steps the administrator should take to resolve the problem

A) Check the source and destination IP address of the tunnel configured on the router.
B) Make sure the IP addresses on the ends of the tunnel are not in the same subnet.
C) Make sure the IP addresses on the ends of the tunnel are in the same subnet.
D) Use the show access-list command to verify the routers are properly configured.