Assess students' recall of the major greenhouse gases (CO2, CH4, N2O, H2O vapor, O3, halogenated gases) and require them to identify the primary natural and anthropogenic sources for each, giving brief examples (e.g., respiration and volcanic activity vs. fossil fuel combustion; wetlands vs. agriculture/landfills; soil microbes vs. fertilizer use; evaporation/atmospheric feedbacks vs. land-use change; photochemical formation vs. industrial refrigerants).