Given the task definition and input, reply with output. 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: lungs are used for breathing air by land animals, Fact2: Mammals are animals with lungs, and they breath air., Question: What do mammals breathe? (A) lung (B) Air (C) O2 (D) Gas (E) Carbon dioxide (F) Urea (G) Heat (H) Moisture
B