Why is mean sea level used?

Answer: A — It is a common, fixed reference

Mean sea level is used because it provides a common, fixed reference surface for measuring elevations and depths worldwide. It’s defined as the long‑term average height of the ocean’s surface, which smooths out daily tides, waves, and short-term weather effects. This creates a stable baseline that maps, surveys, construction, and navigation can all reference, making heights comparable from one location to another. There are regional variations due to gravity and crustal movement, and sea level can rise with climate change, but the long-term average remains the practical standard we use as a global benchmark.