Suppose that when the price of good X falls from $60 to $48, the quantity demanded of good Y falls from 10 units to 8 units. Using the midpoint method, the cross-price elasticity of demand is
a. -1.0, and X and Y are complements.
b. -1.0, and X and Y are substitutes.
c. 1.0, and X and Y are complements.
d. 1.0, and X and Y are substitutes.