Many Older Individuals Feel Faint from Low Blood Flow to the Brain

Multiple Choice

Many older individuals feel faint from low blood flow to the brain if they stand up too quickly after lying down.What is the most reasonable explanation for how this problem develops?

A) The heart rate fails to increase quickly enough to provide the extra pressure needed to push the blood against gravity.
B) The muscles in the arteries and arterioles are relaxed and fail to constrict quickly enough to maintain the appropriate blood pressure.
C) The respiratory rate fails to increase quickly enough to provide the extra oxygen needed.
D) The bloodstream fails to release new red blood cells quickly enough to handle the extra demands.