Suppose that the price of doughnuts decreases and that doughnut-holes are a by-product of producing doughnuts. One would expect:
A.the supply of doughnut-holes to increase.
B.the supply of doughnuts to decrease.
C.the quantity supplied of doughnuts to decrease.
D.the quantity supplied of doughnut-holes to increase.
正确答案:the quantity supplied of doughnuts to decrease.