The correct answer is B. Rubeola.

This boy is presenting with typical findings of rubeola (measles or first disease). It is important to note that in measles, an enanthem (Koplik spots are pictured in the image) precedes the development of the classic exanthem: erythematous macules and papules beginning over the forehead, hairline, and behind the ears with subsequent downward progression.

The remaining listed answer choices do not display Koplik spots.

References:

PMID: 28673424