Why is the marginal product of labor likely to increase initially in the short run as more of the variable input is hired? a. initially workers are able to specialize, but after a certain number of workers have been added, gains from specialization will be exhausted and diminishing total returns will set in. b. the marginal product always increases as more labor is hired. c. initially workers are able to specialize, but after a certain number of workers have been added, gains from specialization will be exhausted and diminishing marginal returns will set in. d. initially firms are able to add additional capital for each worker hired. however, after a certain point, it becomes cost prohibitive to do so.