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 govemment pays fishermen to preserve salmon.