Answer: D
Explanation: Because acid rain would not really affect droughts, and acid rain is better than no rain, so A is out of the question. Oil spills usually affect water, and I never heard of a giant oil spill on land, so same with B.
Ocean pollution has absolutely nothing to do with droughts, because Ocean pollution is for the oceans, not land, so only D is left.
Why it's D is because climate change makes the earth hotter, and there is more water evaporating, and more severe droughts.