Carbon dioxide emissions have been linked to increased air pollution. Suppose that, to reduce carbon dioxide emissions, the government limits total carbon dioxide emissions by all factories to 100,000 tons per month. Each individual factory is given the right to emit 100 tons of carbon dioxide, and factories may buy and sell these rights in a marketplace. This is an example of:
a. Command-and-control policy (regulation)
b. Effluent taxation
c. Emissions trading