The Diagram Below Shows the Marginal Costs of Pollution Abatement

The diagram below shows the marginal costs of pollution abatement for two firms, Firm 1 and Firm 2. FIGURE 17- 5
-Refer to Figure 17- 5. Suppose the government requires that each firm abate pollution to the level Q3. The outcome would be efficient because

A) the marginal cost and marginal benefit of pollution abatement are equated.
B) the marginal costs of abatement are equated for the two firms.
C) the maximum amount of pollution is being abated at the lowest cost.
D) all of the above.
E) none of the above; the outcome would be inefficient.