What Is the Most Likely Reason That Cellular Respiration Would

What is the most likely reason that cellular respiration would shift from an aerobic state into an anaerobic state?

A) The individual was exercising at a level beyond their capability and entered into oxygen debt.
B) A smoker has developed emphysema and has decreased lung capacity.
C) The individual has had a stroke in the left hemisphere of their brain.
D) None of these reasons could cause an individual to shift into an anaerobic state.
E) All of the choices are reasons that an individual could shift into an anaerobic state.