IDNLearn.com provides a comprehensive solution for all your question and answer needs. Discover reliable answers to your questions with our extensive database of expert knowledge.
Answer:
Primary sources can be used directly, as they appear in the natural environment: coal, oil, natural gas and wood, nuclear fuels (uranium), the sun, the wind, tides, mountain lakes, the rivers (from which hydroelectric energy can be obtained) and the Earth heat that supplies geothermal energy.