Classify the following pollution-control policies as command-and-control or market incentive based.

a. A state emissions tax on the quantity of carbon emitted by each firm.

b. The federal government requires domestic auto companies to improve car emissions by 2020.

c. The EPA sets national standards for water quality.

d. A city sells permits to firms that allow them to emit a specified quantity of pollution.

e. The federal government pays fishermen to preserve salmon.