If the demand for product Z is perfectly inelastic, then the corresponding price-consumption curve will be
a. horizontal if the quantity of Z is measured on the horizontal axis
b. upward sloping if the quantity of Z is measured on the horizontal axis
c. downward sloping if the quantity of Z is measured on the vertical axis
d. vertical if the quantity of Z is measured on the horizontal axis
e. downward sloping if the quantity of Z is measured on the vertical axis