Which statement about carbon dioxide and methane is correct?
- Acarbon dioxide: formed when vegetation decomposes; methane: not formed when vegetation decomposes
- Bcarbon dioxide: greenhouse gas; methane: greenhouse gas
- Ccarbon dioxide: not present in unpolluted air; methane: not present in unpolluted air
- Dcarbon dioxide: not produced during respiration; methane: produced during respiration