Which catabolic processes may have been used by cells on ancient Earth before free oxygen became available?
A) glycolysis and the citric acid cycle only
B) glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation, using an electron acceptor other than oxygen
C) glycolysis, pyruvate oxidation, and the citric acid cycle
D) oxidative phosphorylation only
E) glycolysis and fermentation only
Answer: B