Which of the following is true?
A.
Wood burning is a good way to avoid air pollution because it does not burn fossil fuels.
B.
Trucks and buses must meet certain air pollution requirements, but at this time, passenger vehicles do not have such requirements.
C.
It is illegal for factories and power plants to release any amount of toxins (air pollution).
D.
It is legal for factories and power plants to release toxins (air pollution) in limited amounts.