Final answer:
The mean blood pressure in the brain of a standing person is lower than the blood pressure at the heart.
Step-by-step explanation:
The mean blood pressure in the brain of a standing person is lower than the blood pressure at the heart.
When a person is standing, the blood has to overcome the force of gravity to reach the brain, resulting in a decrease in blood pressure. The heart has to work harder to pump blood against gravity to the brain, which leads to a higher blood pressure at the heart.
Therefore, option b. is the correct answer.