Question 3
Photosynthesis is described as the principal process releasing oxygen. Why does that matter to things that are not alive?
The right answer is the one marked above.
Because nothing burns without oxygen. Combustion needs it just as aerobic respiration does. Every fire, engine and furnace runs on gas that came out of a leaf.
The word in the definition is principal, not only. Oxygen enters the atmosphere by other routes too, in far smaller quantities.