Question

photosynthesis is important to living organisms because it is the foundation of most food chains. the source of nitrogen gas in the air. how animals get carbon dioxide to breathe. the process that occurs in most ecosystems.

Explanation:

Photosynthesis by plants produces food (glucose) which forms the base of most food - chains as primary producers are consumed by herbivores and then by carnivores. Nitrogen gas in the air comes from nitrogen - fixing processes and the atmosphere's composition. Animals breathe in oxygen and release carbon dioxide. Photosynthesis occurs mainly in plants in ecosystems but not the only process occurring.

Answer:

A. the foundation of most food chains.