The Figure Shows the Unregulated Market for a Pesticide, Where

Multiple Choice

The figure shows the unregulated market for a pesticide, where S is the supply curve and D is the demand curve. The demand curve is the same as the MSB curve. When factories produce the pesticide, they also create waste, which they dump into a lake on the outskirts of the town. The marginal external cost of the dumped waste is equal to the marginal private cost of producing the pesticide.
-In the figure above, what is the efficient quantity of pesticide to produce?

A) 300 tons per month
B) 240 tons per month
C) 180 tons per month
D) 360 tons per month