Marginal revenue (MR) is _____ when demand is elastic, _____ when demand is unit-elastic, and _____ when demand is inelastic.

(A) zero, positive, negative
(B) zero, negative, positive
(C) positive, negative, zero
(D) positive, zero, negative

The answer is: (D) positive, zero, negative
Marginal revenue (MR) is positive when demand is elastic, zero when demand is unit-elastic, and negative when demand is inelastic.