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
A person unacclimitised develops pulmonary edema in 
Select and explain. 
A. 2 - 3 days, B. 6 -7 days, C. 19 - 21 days, D. 2nd - 3rd month
A: 2 - 3 days
Answer: A: 2 - 3 days 
Explanation: 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.