During exercise, stimulation of the TCA cycle results principally from which one of the following?
选项：

A:Allosteric activation of isocitrate dehydrogenase by increased NADH
B:Allosteric activation of fumarase by increased ADP
C:A rapid decrease in the concentration of four-carbon intermediates
D:Product inhibition of citrate synthase
E:Stimulation of the flux through several enzymes by a decreased NADH/NAD+ ratio