Answer:
The answer is A: oxygen
Step-by-step explanation:
Photosynthesis mainly occur in plants. It is a process by which plants glucose from carbon dioxide and water in the presence of chlorophyll. The reaction of photosynthesis is as below:
Carbon dioxide + water -------------> Glucose + oxygen.
As you can see in the reaction the main output of this process is oxygen which is liberated into the environment and glucose (source of energy) which is used for metabolism in plants.