Using the midpoint method, the price elasticity of demand for walnuts between the price levels of $15 and $9 per ton is ____, meaning that between these two points, demand is ____. Thus, you can conclude that the grower's claim is ____, because total revenue will ____ due to the technological improvement.
a. inelastic; decrease; valid; increase
b. elastic; increase; invalid; decrease
c. unitary; unchanged; valid; stay the same
d. elastic; increase; valid; increase