Final answer:
A guide is a continuous mark used by hair stylists to create the desired haircut, while an outline in art defines the edges of objects, giving the impression of form and depth.
Step-by-step explanation:
A guide is a thin, continuous mark, curved or straight, used as a guide while cutting hair. The correct option is D) Guide. In the context of haircutting, a guide is a reference point established that stylists follow along to create the desired hair length and shape. This concept can be juxtaposed with artistic principles, such as the use of outline in drawings and sketches.
An outline is a heavy, often black, contour line that defines the edge of an object or figure, setting it apart from the background or other objects. It forms the outer edge of a silhouette, or the line made by the edges of an object. For example, on a piece of art, an outline helps to create a sense of form and can contribute to the perception of depth and three-dimensionality, simulating shadows and highlights, much like the hatching on the left side of a character's hat, which indicates it is in shadow.