Which of the following statements is not correct?

a.

Monopolistically competitive firms engages in non-pricing competition

b.

Purelymonopolyand monopolistically competitive firms, face a downward sloping demand curve.

c.

In the long run purely competitive firms and monopolistically competitive. firms earn zero economic profits, while pure monopolies may or may not earn economic profits

d.

Purely competitive firms, monopolistically competitive firms, and pure monopolies all earn zero economic profits in the long run.