Answer:
A circular network happens when you have two (or more) routes to the same controller. Typically, the routes are BACnet/IP and BACnet/Ethernet and both are communicating on both networks. This could happen with BACnet MS/TP although it is rare.
Explanation:
I believe it is a large network of roads sorry if I am mistaken
The answer is D, because it's called a back-up.