Answer:
The correct answer is - the difference in altitudes.
Explanation:
The hemoglobin in the person of Denver who lives at a higher altitude than the person who lives in Philadelphia will be much higher. This is due to the fact that at higher elevation or altitude atmospheric pressure decreases that causes hemoglobin to stick to the RBCs and that results in less oxygen level in the body.
To compensate for this low level of oxygen levels hemoglobin content need to be higher in people living at a higher elevation.
