about twenty percent of the world's present energy comes from the sun in one form or another. Special devices have already been made available to put on the roofs of houses and flats to catch the sun's rays and thus heat water. Thousands of these devices are now being used to provide energy in homes throughout the United States while more than a million solar water-heating units have already been built in homes in Japan. Other purposes for which solar energy is at present, being used include the separation of salt from seawater, irrigation and sewage disposal. For most people in developing countries, the need is not air-conditioners or central heating, but for cheap ways of cooking food, drying crops, and lighting house.
1.what have people made to help houses and flats to catch the sun's rays?
2.where have people built more than a million solar water-heating untis?
3.is the solar energy being used to remove salt from seawater at present?
4.what do people in developing countries need?
