The citric acid cycle (cac) is activated in the presence of oxygen, but what is the link between the cac and oxygen? pick the one best choice: a. oxygen is an allosteric activator for citrate synthase. b. the presence of o2 in the mitochondrial matrix releases co2 into the cytosol. c. the one substrate-level phosphorylation in the cac can occur in the absence of oxygen. d. the major product of the cac is nadh, the principle electron donor to the o2 , the last electron acceptor in the electron-transport system. e. the major product of the cac is fadh2 , the principle electron donor to the o2 , the last electron acceptor in the electron-transport system.