The answer is (b) climb... I think its the "TAT" that is causing confusion, I think we can all agree in the question we are flying through the tropical jetstream, so when flying through a jetstream the OAT is constant... but does the TAT increase? "To minimise the risk of encountering CAT the pilot should?" I think that we can agree that descending is not an option because the CAT area is on the polar side(where we are tracking) below the jet core... I guess climbing would minimise the risk of encountering the CAT as we would be climbing out above the jetstream above the CAT on the polar side... changing track to left or right wouldnt really do anything I guess so by RTFQ rationale the most logical answer could be climb even tho the scenario is quite strange. But I still dont know why the TAT is increasing while we are maintaining FL370 whilst in the jetstream.. if anyone can answer that Ill take my hat off to them!