As Sarai hires more and more workers under the same limited office space, Sarai expects to see a decline in the marginal product of workers which is known as the [ Select ] If Sarai's hires a 5th worker who can produce an additional 40 client services per work-day, this is the [ Select ] of the 5th worker, and if all 5 workers' production is 300 client . services per work-day, this is the [ Select ] of 5 workers. If the 20th client service unit costs $12 to produce, this is known as the [ Select ] Some resources can be fixed in the [ Select ] but all resources must be variable in the [ Select ] If Sarai's business expands enough, in the long run she might experience lower average cost as she ramps up production, which is called [ Select ] or experience higher average cost as she ramps up production, which is called [ Select ]