Final answer:
During moderate exercise, the blood flow to the brain stays relatively constant because the brain's blood vessels do not possess receptors that respond to exercise stimuli.
Step-by-step explanation:
During moderate exercise, cerebral blood flow mainly remains unchanged. This is due to the fact that blood vessels in the brain largely do not respond to regulatory stimuli associated with exercise, because they often lack the necessary receptors to do so. Despite changes in cardiac output and redistribution of blood flow to other parts of the body such as skeletal muscles and heart during physical activity, the brain's requirement for a constant supply of oxygen and nutrients necessitates that its blood flow is maintained at a stable rate.