Paddy fields are anthropogenic sources of both nitrous oxide (N2O) and methane (CH4). These are reckoned as 273 and 80-83 times more powerful than CO2 respectively in driving temperature increase over 20 years. Paddies are a potential source of anthropogenic N2O emission from both the soil and the rice plants. Methane is produced in the anaerobic conditions of flooded paddy fields. Hence rice is the correct answer.