TOEFL Reading: ETS-TOEFL阅读机经 - 0363K3DU266K4B3SL$

Paragraph 3 suggests which of the following about the process of photodissociation? A. It is more common today than it was in the early history of the atmosphere. B. It is responsible for only a small amount of the oxygen in the atmosphere today. C. It removes trace amounts of oxygen from the atmosphere. D. It produces more free oxygen than photosynthesis does.