This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'A mountaineer ascents 18,000 feet in 2 days without supplemental oxygen. At the height of ascent the changes area) ↑ed PaCO2b) ↓ed Barometric pressurec) ↓ed Inspired O2 d) ↓ed PaO2e) ↑ed pH \nSelect and explain. \nA. abc, B. ade, C. bde, D. bce', 'role': 'user'}, {'content': 'Answer: C \nExplanation: At high altitude, the atmospheric pressure is low and partial pressure of O2 in air is low. This results in decreased PaO2, though the fraction of inspired air remains same. Hyperventilation results in CO2 washout and respiratory alkalosis.', 'role': 'assistant'}]