The perfectly competitive firm, whose marginal revenue and marginal cost curves are shown, should produce

A$.9$ units, since that is where its profits will be maximized.

B$.40$ units, since that is where MC $=MR$ and MC is decreasing.

C$.9$ units, since that is where $MC=MR.$

D$.40$ units, since that is where MC $=$ MR and MC is increasing.

E$.$ either $9$ or $40$ units, since MC $=$ MR at both levels of production.

F$.$ at the minimum point of the MC curve.