Final answer:
A 3-D form has height, width, and depth as its spatial measurements. 'Depth' is the correct answer to fill in the blank for the third spatial dimension, distinguishing it from height and width. Volume can be calculated using these three measurements.
Step-by-step explanation:
Because it's 3-D, a form has these three spatial measurements: height, width, and depth. Depth is the third dimension in a three-dimensional space, alongside height and width. These measurements together define the size and shape of a physical object or space. Length is typically considered to be synonymous with depth in many contexts, but in distinguishing from other dimensions, depth refers specifically to the measurement from front to back.
The term mass is related to the overall amount of matter in an object and is not a spatial measurement. Thus, for questions about spatial dimensions, 'mass' would not be the correct term to complete the series of height, width, and depth.
Furthermore, volume can be determined by multiplying the measurements of height, width, and depth. If you know the length of each side of an object, you can calculate its volume, which is the space it occupies. For example, in a rectangular prism, the volume is found by multiplying its height, width, and depth (length).