The earliest organisms were completely heterotrophic in nature. Why?

A. The primitive atmosphere lacked sunlight. Primitive organisms did not have a system complex enough to use for other sources for photosynthesis.
B. The primitive atmosphere lacked oxygen. Primitive organisms did not have a way to break down the oxygen in water.
C. The primitive atmosphere lacked carbon dioxide. Primitive organisms did not have a way to obtain carbon dioxide for photosynthesis.