Final answer:
Low air pressure is usually associated with high-altitude areas or places with low density or less air molecules. The lowest air pressure would be experienced in a hot-air balloon high in the sky.
Step-by-step explanation:
Low air pressure is usually associated with high-altitude areas or places with low density or less air molecules. Based on this, the correct answer would be B. In a hot-air balloon high in the sky. When a hot-air balloon rises, it enters regions of lower air pressure due to the decrease in density at higher altitudes.
On the other hand, A. In a valley would not have the lowest air pressure because the surrounding air exerts pressure and pushes down into the valley. Similarly, C. In an underground cave would also have higher air pressure due to the weight of the overlying rocks and earth.
D. On a sailboat way out in the ocean does not have the lowest air pressure either. While it may be far from land, the air pressure is not significantly affected by its location in the ocean as it is influenced by altitude rather than proximity to land or water.
Learn more about Air pressure