Ключевые слова: alternative, blackboard, board, business, chalk, chalkboard, clean, co2, concept, conservation, development, earth, eco, ecological, ecology, education, energy, environment, environmental, friendly, global, globe, green, greenhouse, healthy, industrial, learn, natural, nature, organic, oxygen, planet, plant, power, recycle, recycling, reduce, renewable, resources, reuse, save, school, solar, sustainable, symbol, turbine, urban, warning, wind, world,