Pre-thinking: Since the program was announced, the water level at all three reservoirs has returned to normal. It means, there is relation between Action (save water program) and Result (Water level back to normal in reservoir) .
Which of the following, if true, casts the most doubt on the efficacy of the officials’ program?
(A). The current water level in the reservoirs is lower than it was at the same time last year. -> It doesn't connect with the program. Incorrect.
(B). Other nearby reservoirs recovered from lower water levels this year, even though those reservoirs provide water to cities that did not enact water restriction policies. -> It means, without programs in place, water level came back to Normal in reservoir. So, what is the use of such programs. Let's keep it.
(C). Residents reduced their water usage for lawn maintenance significantly more than they did for washing clothes. -> It means program is working. Incorrect.
(D). Imposing stiff penalties on residents who did not conserve water would have resulted in even higher water levels in the reservoirs. -> It is another way to get program working.
(E). Water usage in the city dropped steadily during the first two weeks of the program before leveling off. -> Incorrect. No idea, how the program is impacting water saving.
So, I think B.