Device count should be more than 1.

Redundant trunk groups are designed to provide link redundancy. If the primary link fails, the secondary link will automatically take over to ensure continued connectivity.
In redundant trunk groups, while regular data traffic is sent over the primary link, Layer 2 control traffic (such as STP, LACP, etc.) is allowed on the secondary link to maintain network stability and protocol operations.
https://www.juniper.net/documentation/us/en/software/junos/multicast-l2/topics/topic- map/redundant-trunk-groups.html

Option A is correct. For traffic to be sent through a GRE tunnel, there must be a route that directs the traffic into the tunnel. This is typically accomplished through the use of a static route or a dynamic routing protocol.
Option B is correct. All intermediary devices must have a route to the tunnel endpoints. In real- world scenarios, the tunnel endpoints for a tunnel going over the Internet must have globally reachable internet addresses. Otherwise, intermediate routers in the Internet cannot forward the tunneled packets.