In a Market with External Costs, Suppose the Efficient Level

In a market with external costs, suppose the efficient level ofoutput is 1,000 units. Which of the following statements isTRUE?

A) To achieve the efficient level of output, the government should set a subsidy equal to the external cost.
B) To achieve the efficient level of output the government could set a tax equal to the external cost or issue enough tradeable
Allowances to restrict the output to the efficient level.(True
Answer ) Correct
C) With external costs, the government can use only taxes to achieve the efficient level of output.
D) With external costs, the government can use only tradeable allowances to achieve the efficient level of output.