Answer:
The correct answer would be option a. 3
Step-by-step explanation:
When lung exposed to a high altitude like Mt. Everest, it shows elevated heart rate, faster breathing due to hyperventilation so it could get enough oxygen supply to its tissues.
The oxygen level at sea level are three time more than the oxygen level at Mt. Everest as oxygen level is 30 to 33 percent of the seal level.
Thus, the correct answer is : option a. 3.