Recently some colleges and private companies have launched free online courses that can be taken by anyone with an Internet connection. The most successful of these "massive open online courses" (MOOCs) have attracted tens of thousands of students. An article in the Economist magazine discussing MOOCs observed: "Though marginal costs are low, designing enticing online material is costly." Why would the marginal costs of offering a MOOC be low? What is the relationship between the marginal costs, average fixed costs, and average total costs of offering a MOOC? Draw a graph to illustrate your answer.