When the law of diminishing returns takes effect   a. a firm must always try to add the same amount of input to the production process. b. more input must be added in order to increase its output. c. firms must add decreasingly more input if they are to maintain the same extra amount of output. d. firms must add increasingly more input if they are to maintain the same extra amount of output.

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The law of diminishing marginal returns states: Select one: a. As a firm uses more of a variable factor of production, total product (TP) eventually decreases. b. As the size of a plant increases, marginal product (MP) eventually decreases. c. As a firm uses more of a variable factor of production, its average cost (AC) eventually decreases. d. As a firm uses more of a variable factor of production, with a given quantity of the fixed factor of production, the MP of the variable factor eventually decreases.