Compared to a command and control government approach to reducing pollution, a market-based system of tradable pollution allowances is:

a. more efficient because polluters that can only reduce pollution at high cost do not and instead buy allowances.

b. less efficient because pollution allowances are "licenses to pollute."

c. more efficient because the bulk of the pollution reduction is carried out by those who pollute the most.

d. less efficient because polluters are not required to reduce pollution by the same amount.

e. more efficient because polluters have the same cost of reducing pollution.