In the United States SO₂ Program, Emissions Permits Are Tradable

In the United States SO₂ program, emissions permits are tradable and managers of a particular plant can

A) emit at or below the plant's allowable level and hold on to any excess permits
B) emit below the plant's allowable level and sell off any excess permits
C) emit above the plant's allowable level and purchase permits to cover the excess emisisons
D) all of the above are allowable options