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").

Fact1: Cartilage is a tough tissue that contains a protein called collagen., Fact2: Sharks have a cartilage skeleton., Question: What has skeleton made of tough tissue that contains a protein called collagen? (A) mammals (B) rocks (C) animals (D) sharks (E) a fish (F) cows (G) humans (H) plants
D