Which of the following best describes how deep something is?

Depth is the most appropriate term to describe how deep something is because it specifically refers to the measurement of how far down something extends from a surface to a point below it. In oceanography, for instance, depth is often used to describe how deep bodies of water are from the surface to the seabed, or how deep geological features are when exploring underwater.

The other terms do not accurately convey the same meaning. Altitude refers to the height of an object in relation to sea level or ground level, typically used for objects above the Earth's surface. Magnitude is a term that usually describes the size, extent, or importance of something, often used in the context of energy or earthquakes rather than physical dimensions. Height, while it describes the vertical measurement of an object from base to top, applies primarily to objects above a reference point, such as sea level, rather than below it. This distinction makes depth the clear and correct choice for describing how deep something extends.