Biologists Believe That Earth's Early Life-Forms Were Exposed to an Atmosphere

Multiple Choice

Biologists believe that Earth's early life-forms were exposed to an atmosphere with no molecular oxygen and had not yet evolved the Krebs cycle. If so, alcoholic fermentation would have been particularly critical to life because without the pathway

A) ethanol would not be available as a nutrient for other consumers.
B) lactic acid would accumulate and disable prokaryotic muscle cells.
C) carbon could not be recycled back into the biosphere for use by producers.
D) the only source of NADH for electron transport would be from glycolysis and ATP production would be greatly reduced.