Refer to the figure below. At point D, the opportunity cost of making milk is:

A.high because productive resources that are better-suited to making movies are not being used to make milk.

B.low because the economy is specializing in making milk.

C.high because the economy is not operating efficiently.

D.high because productive resources that are better-suited to making movies are being used to make milk.

正确答案：high because productive resources that are better-suited to making movies are being used to make milk.