Answer
Option: d. Workers are of equal quality.
Work Step by Step
The law of diminishing returns assumes that all units of labor are of equal quality. Each successive worker is presumed to have the same innate ability, motor coordination, education, training, and work experience. Marginal product ultimately diminishes, but not because successive workers are less skilled or less energetic. It declines because the firm is using more workers relative to the amount of plant and equipment available.
