Detailed Instructions: In this task, you are given two facts, and a multiple-choice question. Based on the given facts, answer the question with index of the correct option (e.g, "A").
Q: Fact1: Many corals secrete an exoskeleton that builds up to become a coral reef., Fact2: To fisherfolk, coral reefs are homes to fish that are waiting to be caught., Question: What do exoskeletons secreted by corals do? (A) Give homes to humans (B) Give homes to penguins (C) competing for resources (D) Give homes to fish (E) reproduce (F) Give homes to birds (G) preventing heat transfer (H) protect them
A:
D