The correct answer is C. Four pies
Step-by-step explanation:
Marginal cost refers to an increase in the cost of production as additional units are made. In the case of apple pies, the graph shows the cost for one is $1.00. Moreover, this decreases when two or three pies are produced because the cost is between $0.60 and $0.30. However, if the producer makes four or more units, the cost increases. For example, at four units the cost per unit is $0.60, while at six units the cost is $1.50. Thus, the marginal cost begins to increase at four pies.