The monopolistic competitive firm sells product and faces demand curve.
a. a homogeneous; a horizontal
b. a differentiated; a horizontal
c. a differentiated; a downward-sloping
d. a homogeneous; a downward-sloping

d. a homogeneous; a downward-sloping

Explanation:

The monopoly is a market structure where there is a single bidder of a certain good or service, that is, a single company dominates the entire supply market, and there is a homogeneous product or there are no nearby substitutes. When there is a monopoly in a market, there is only one company capable of offering a product or service that does not have close substitutes.

The monopoly faces a negative slope demand curve: depending on the price set buyers will demand more or less.

this is not a question

answer; can each be concretely realized in different ways;