Option A: Water boils at temperatures below 100°C at high altitudes because atmospheric pressure decreases. At higher altitudes, the column of air above is shorter, resulting in lower atmospheric pressure. Since boiling occurs when the vapor pressure of a liquid equals the atmospheric pressure, the reduced atmospheric pressure means water molecules can escape the liquid phase more easily, causing it to boil at lower temperatures. This principle is why water boils faster in a pressure cooker, where increased pressure raises the boiling point. Options B and C are incorrect; gravity’s slight variation with altitude or wind patterns don’t significantly affect water’s boiling point. Therefore, the correct explanation lies in the decrease in atmospheric pressure, which directly impacts the boiling point of water at high altitudes.