Choices: 1). glucose; 2). hydration; 3). sunlight; 4). scandium; 5). recovery; 6). oxygen; 7). uranium; 8). radon;

Fact 1: Oxygen is essential for cellular respiration for all aerobic organisms. Fact 2: Cellular respiration is a requirement for life. Given the two facts above, which is a requirement for life?
Answer:
6).