"in order to reduce the amount of air pollution in pennsylvania, which change is necessary?
(1)laws must be passed to protect endangered species.
(2)the use of natural resources must be increased.
(3)more coal-burning power plants must be built.
(4)the cooperation between the different states must be improved."

One change to reduce the amount of air pollution in the state of Pennsylvania is the cooperation between all of the different states must be improved. Without the other states doing something to prevent the air pollution, it will keep spreading to the other states. This is something that the government has been trying to achieve for several years. The correct answer choice is 4.