Which principle directs the viewer's attention first to a particular part of an artwork?

Correct answer: Emphasis

The governing principle is emphasis. In visual art, emphasis directs the viewer’s attention to a chosen area by using differences in colour, size, placement, contrast, detail, or isolation. That area becomes the focal point, so option C is correct. Balance distributes visual weight, rhythm creates movement through repetition, and harmony produces a sense of agreement among elements; none of those definitions specifically means directing attention first to one part.