The Estimated Demand for a Good X Is $\hat { Q } = 70 - 3.5 P - 0.6 M + 4 P _ { Z }$

Multiple Choice

The estimated demand for a good X is $\hat { Q } = 70 - 3.5 P - 0.6 M + 4 P _ { Z }$ ,where $\hat { Q }$ = units of the good,P = price of the good,M = income,and $P _ { z }$ = price of related good Z.All parameter estimates are statistically significant.Which of the following statements is correct?

A) X is a normal good.
B) X is an inferior good.
C) X and Z are substitutes.
D) X and Z are complements.
E) both b and c