Answer the following question: Fact 1: Lungs are used for breathing air by land animals. Fact 2: Mammals are animals with lungs, and they breath air. Given the two facts above, what do mammals breathe?

Available choices:
1). lung;
2). Air;
3). O2;
4). Gas;
5). Carbon dioxide;
6). Urea;
7). Heat;
8). Moisture;
Answer:
2).