The Marginal External Cost Associated with Air Pollution Increases with the Annual

The marginal external cost associated with air pollution increases with the annual output of a polluting industry. At the current competitive equilibrium level of output per year, the marginal external cost is $10 per unit of output. To achieve efficiency,

A) a corrective tax of $10 per unit of output is required.
B) a corrective tax of more than $10 per unit of output is required.
C) a corrective tax of less than $10 per unit of output is required.
D) a corrective subsidy of $10 per unit of output is required.
E) a corrective subsidy of less than $10 per unit of output is required
)