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1: Active solar heating system 2: Soil 3: Community 4: Human 5: Feeder 6: Water 7: Lead 8: Range 9: Environment 10: Current 11: Condition 12: Process 13: Atom 14: Carbon 15: Contamination 16: Electricity 17: Plant 18: Fishery 19: Hazard 20: Conservation (As of 17:21)