Read and choose the best answers to the following questions.
Energy is fundamental to human beings, especially to poor people – the one- third of humanity that does not have modern energy supplies like electricity, with which their life could be improved.
Many people who live in the countryside have to gather fuel wood. This takes a lot of time. Moreover, it causes indoor air pollution because of heavy smoke. For many people living in rural areas in developing countries of the world, biogas is the largest energy resource available and costs almost nothing. The main use of biogas is for cooking and heating. As biogas is smoke-free, it helps solve the problem of indoor air pollution. Moreover, plant waste and animal manure cost almost nothing.
The tendency to use renewable energy sources is on the increase when non-renewable ones are running out. In the near future, people in developing countries may use wind or sea waves as the environment-friendly energy sources.

What is the main use of biogas?