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Subject
- Conservation of natural resources237
- Natural resources124
- Environmental protection106
- Economic aspects86
- Environmental aspects78
- Environmental policy78
- Water77
- Pollution63
- Refuse and refuse disposal53
- Toxicology53
- Effect of human beings on49
- Human ecology49
- Nature49
- Waste disposal49
- Land use48
- Management40
- Business ethics38
- Human geography36
- Environmental geography29
- Power resources29