This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Physiology
[{'content': 'A person unacclimitised develops pulmonary edema in \nSelect and explain. \nA. 2 - 3 days, B. 6 -7 days, C. 19 - 21 days, D. 2nd - 3rd month', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A small percentage of people who ascend rapidly to high altitudes become acutely sick and can die if not given O2 or rapidly moved to a low altitude. The sickness begins from a few hours up to about 2 days after ascent. Two events frequently occur. Acute cerebral edema and acute pulmonary edema.', 'role': 'assistant'}]