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: lungs are used for breathing air by land animals, Fact2: Inside of the lungs are little sacks called alveoli., Question: What are used for breathing air by land animals? (A) Frogs (B) pigeons (C) gills (D) alveoli (E) fish (F) ferns (G) four limbs (H) water
A:
D