Among the following crops, which one is the most important anthropogenic source of both methane and nitrous oxide ?

Rice is the correct answer because its cultivation in flooded, anaerobic conditions facilitates methanogenesis (methane production), while the heavy use of nitrogenous fertilizers in these waterlogged fields leads to significant nitrous oxide emissions through denitrification. While crops like sugarcane and wheat are major consumers of nitrogen fertilizers (sources of $N_2O$), they are typically grown in well-aerated soils and do not contribute significantly to methane production. The core concept tested is the impact of specific agricultural practices and biogeochemical processes on greenhouse gas (GHG) emissions.