Final answer:
The third spatial measurement for a three-dimensional form, besides height and width, is depth.
Step-by-step explanation:
Because it is three-dimensional, a form has these three spatial measurements: height, width, and depth. The correct answer to complete the sentence is C) Depth.
Length is the measurement of the extent of something along its greatest dimension. The SI basic unit of length is the meter (m), which is used to measure linear dimensions in a single direction. In contrast, depth usually refers to the measure of how far back an object extends, or how deep it goes, which is a different direction than length or width and completes the three-dimensional aspect of an object for geometrical measurements or volume calculations.