Concept:A curve that rises, reaches a peak, and then falls describes the total product curve.Explanation:As more units of the variable input are added, total output first increases.After a point, output rises at a decreasing rate and eventually starts to fall when marginal product becomes negative.This behaviour gives the total product curve its characteristic upward-then-downward shape.The curve labelled x therefore cannot be a revenue curve, since revenue curves show price-and-quantity relationships, not production levels.Answer:B. total product curve
