Detailed Instructions: You are given a science question (hard-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.
Q: A population of deer recently increased in size. Which most likely could have caused the deer population to increase?
(A) A disease was spreading. (B) Their habitat was destroyed. (C) Food sources were hard to find. (D) Their predators were disappearing.
A:
D