Some microorganisms, such as yeast, produce energy in oxygen-free environments through the process of A. mitosis. B. photosynthesis. C. aerobic respiration. D. anaerobic respiration.

D. anaerobic respiration. Yeast produces energy in an environment without oxygen through the process of fermentation, an example of anaerobic respiration. The word anaerobic means "living without air". Yeast produces ethanol and carbon dioxide from glucose through anaerobic respiration.