An environmental study conducted in a particular city suggests that if a chemical plant emits more than 60 million tons of chemicals each year, the water supply will become contaminated beyond the point where filtration techniques can make it safe for drinking.

Explanation:

If the water becomes too contaminated because of the pollutants emitted by the chemical factory that the water can not be filtered to make it safe for drinking.

The only solution to check the pollution contamination in the water is by tradable permit.

By imposing tradable permit, the government put a control to the chemical industries to limit their production so that not pollutants goes to the water and water does not become incompatible for filtration. By this they can limit the pollution in water.

Thus the answer is tradable permit.

the correct answer is c.