GWD 11-40

Q40:
Parland’s alligator population has been declining in recent years, primarily because of hunting.  Alligators prey heavily on a species of freshwater fish that is highly valued as food by Parlanders, who had hoped that the decline in the alligator population would lead to an increase in the numbers of these fish available for human consumption.  Yet the population of this fish species has also declined, even though the annual number caught for human consumption has not increased.

Which of the following, if true, most helps to explain the decline in the population of the fish species?

A. The decline in the alligator population has meant that fishers can work in some parts of lakes and rivers that were formerly too dangerous.
B. Over the last few years, Parland’s commercial fishing enterprises have increased the number of fishing boats they use.
C. Many Parlanders who hunt alligators do so because of the high market price of alligator skins, not because of the threat alligators pose to the fish population.
D. During Parland’s dry season, holes dug by alligators remain filled with water long enough to provide a safe place for the eggs of this fish species to hatch.
E. In several neighboring countries through which Parland’s rivers also flow, alligators are at risk of extinction as a result of extensive hunting.
 

Answer: D

I chose B and I knew that B might be wrong. But I am quite puzzled about answer D. Can anyone explain it to me? Thank you. 

My friend helps me find the answer. Maybe I am lack of that sort of logical brain. Actually it is easy, but I just couldn't get it.

In D, it gives the explanation that the existence of alligator can help to give a safe place for the hatch of that fish egg. Because the alligators become less and less, the fish eggs don't have that safe places to reproduce,  so the fish becomes less and less too.