Assess students' understanding of the carbon cycle by requiring identification of major natural reservoirs (atmosphere, oceans, terrestrial biomass, soils/sediments), explanation of key fluxes and processes (photosynthesis, respiration, decomposition, ocean uptake, fossilization), basic comparison of flux magnitudes and timescales, and analysis of how human activities (fossil fuel burning, deforestation, land-use change) alter fluxes and increase atmospheric CO2; include interpretation of a simple diagram or time-series data.