Which of the following is true about a carbon emissions tax? (Select all correct answers)

a) A firm has an incentive to reduce emissions as long as its marginal cost of reduction is lower than the tax.

b) A firm would pay the tax rather than reduce emissions if its marginal reduction costs are higher than the tax.

c) A tax on emissions guarantees that a reduction goal will be achieved.

d) A tax provides certainty about the future price on carbon.