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: Most mollusks have shells., Fact2: Mussels are bivalve mollusks., Question: Mussels have what? (A) seaweed (B) arms (C) Energy (D) a shell (E) warmth (F) bacteria (G) Length (H) legs
A:
D