Correct Answer - C
Considering a projected length 2R on the ring in verticle plan. This length will move at a speed v perpendicular to the field.
This results in an induced emf:
In Ring "A" : `e_(A)`= BV(2R)
In Ring "B" : `e_(B)` = B(V)(2R) ltBrgt `therefore` potential difference between upper polints
=BV(2R) + BV(2R)=4BVR