Definition: 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").
Input: Fact1: a breathing mask is used for keeping harmful particles from entering the respiratory system, Fact2: Another respiratory defense is the immune system., Question: the what is a defense against harmful particles from entering the body (A) lungs (B) It remains dormant (C) A virus (D) immune system (E) exoskeleton (F) pancreas (G) chickenpox (H) liver
Output:
D