Final answer:
Jill will live at high altitude because increased red blood cell count helps in oxygen transport at high altitude.
Step-by-step explanation:
Jill will live at high altitude because of option a) Increased red blood cell count helps in oxygen transport at high altitude. In response to lower oxygen levels at high altitudes, the body produces more red blood cells to compensate. This increase in red blood cells helps to transport oxygen more efficiently throughout the body.