In a recent study of stroke patients, those who exhibited continuing deterioration of the nerve cells in the brain after the stroke also exhibited the highest levels of the protein glutamate in their blood. Glutamate, which functions within nerve cells as a neurotransmitter, can kill surrounding nerve cells if it leaks from damaged or oxygen-starved nerve cells. Thus glutamate leaking from damaged or oxygen-starved nerve cells is a cause of longterm brain damage resulting from strokes. Which one of the following, if true, most strengthens the argument? ['Stroke patients exhibit a wide variety of abnormal chemical levels in their blood.', 'Glutamate is the only neurotransmitter that leaks from oxygen-starved or physically damaged nerve cells.', 'Leakage from damaged or oxygen-starved nerve cells is the only possible source of glutamate in the blood.', 'Any neurotransmitter that leaks from a damaged or oxygen-starved nerve cell will damage surrounding nerve cells.']