The marginal revenue product of a resource: Select one: a. is defined as the marginal product of the resource multiplied by the resource price. b. simply means that a firm should add to its capital stock as long as competition requires it. c. equals the extra output produced by an additional unit of the resource multiplied by the price of that output. d. equals the average product of the resource multiplied by the cost of hiring an additional (marginal) unit of the resource