The Fresh Kills Landfill in Staten Island, New York, is in the process of becoming the Fresh Kills Park. Gas left over from the landfill underneath will be siphoned off or burned for domestic energy use. Which statement best describes the environmental consequence of the sustainable use of landfill gas?

I. Landfill gases release mercury when burned.
II. Landfill gases create smelly odors for residents.
III. Burning landfill gas causes air pollution.

III only
I and II
II and III
I, II, and III