Which certification are you studying for? Reading the question it clearly states:
"...multiple copies of the SAME unicast frame LIKELY to be transmitted in a switched LAN?"
If you're studying for the latest CCNA version, it's very very dull information regarding Ring topologies...it's as you may have noticed focused on Ethernet and Star topologies.
I agree with CiscoLoco, answer B is correct because STP is most likely not enabled.
Reason: It says in the question that it's using a unicast frame. Then based on the CCNA curriculum it's ethernet, as token ring uses another type of frame called "Token Frame" and also uses Active monitor/standby monitor stations to detect multiple token frames.
Edit: I may (have!!) expressed myself a bit....confusing, so to avoid confusion....token ring uses a different technique than ethernet and stations are added based on a 5-phase process before they can participate in the ring. Token ring still uses broadcast, unicast and multicast - just wanted to make that clear Tamer ! So to not go into details, it's much much more likely a L2 loop will occur in a Ethernet switched network without STP enabled than it it is in a dual token ring topology but it Can occur and STP should be enabled.