Ключевые слова: alternative, background, battery, bio, biofuel, biogas, biological, blue, climate, collection, concept, continent, conversion, earth, eco, ecology, energy, environment, gas, geography, globe, green, house, icon, icons, industry, innovation, mainland, nature, organic, peace, planet, pollution, process, production, recycle, renewable, set, sign, solar, source, symbol, technology, tree, waste, world, world environment day,