7. Suppose the demand for good X is estimated according to: QDX = 12 + .06Px - 0.1Pz-.03Y, where Px represents the price of good X, Pz represents the price of related good Z, and Y represents income. If products X and Z are complements and normal goods, what can be said about the quality of this demand function based on an analysis of the signs of the coefficient values? a. This demand function is accurate in the sense that all coefficients meet expectations for signs b. This demand function is inaccurate because while it meets expectations for the complementary good's price, it fails for its own price and income c. This demand function is inaccurate because while it meets expectations for income, it fails for the complementary good's price and its own price d. This demand function is inaccurate in the sense that all coefficients fail expectations for signs