Why should the role of oxygen in complex life not be limited only to respiration?

Correct answer: Because ozone protection also developed from oxygen

The correct answer is B. Oxygen was important for complex life in two connected ways. First, aerobic respiration uses oxygen to release much more usable energy from food than anaerobic processes, supporting larger, more active, and more complex organisms. Second, oxygen in the upper atmosphere helped produce ozone, a form of oxygen that absorbs much of the Sun’s harmful ultraviolet radiation. This ozone shield made it safer for life to develop and eventually occupy land environments. The other choices are scientifically unrelated: oxygen did not end gravity, form Earth’s core, or dry up the oceans. Therefore, its importance cannot be reduced to respiration alone.