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").
Input: Fact1: a breathing mask is used for keeping harmful particles from entering the respiratory system, Fact2: Air pollution is caused by the build-up of harmful gases and particles in the air., Question: What does a gas mask keep out? (A) disease (B) The atmosphere (C) heat energy (D) air pollution (E) energy barrier (F) Bodily water (G) Dehydration (H) bacteria
Output:
D