Assess students' understanding of the carbon cycle by identifying major natural reservoirs (atmosphere, biosphere, hydrosphere, lithosphere), describing key fluxes and processes (photosynthesis, respiration, decomposition, ocean uptake, sedimentation), comparing relative magnitudes and timescales, and explaining how human activities (fossil fuel combustion, deforestation, land-use change) alter fluxes, shift sources/sinks, and drive climate change; tasks may include labeling diagrams, interpreting simple flux budgets or graphs, and explaining implications for mitigation.