what is the slight curve on the narrow side exhibited by most lumber?\nbow\nswell\nhump\ncrown

Brief Explanations:

In the context of lumber, the slight curve on the narrow side is known as the crown. A bow is a curve along the length of the board, a swell is an increase in size or thickness over a part of the board, and a hump is a localized raised - up area. The crown is the correct term for the described curve.

Answer:

D. crown