The possible answers are
A.a drought reduces the toad population
B. an influx of soil nutrients results in increased grass growth
C.a hawk species moves in that hunts toads
D.the toad population increases after a warm, wet spring
The correct answer is D
The increase in numbers in the toad population after a warm and wet spring would mean that there are more toads that prey on the beetles and that they are limiting the beetle population by hunting them.