Fact 1: An animal requires air for survival. Fact 2: Oxygen Oxygen is in the air we breathe. Given the two facts above, oxygen for survival is necessary for what?

Available options: 1). health; 2). humans; 3). cancer; 4). corpses; 5). cells; 6). pebbles; 7). animals; 8). erosion;
The answer is:
7).