Choose the word or phrase that best fits the blank space in the following passage. from need house collect lighting to provide homes About twenty percent of the world’s present energy already comes from the sun in one form or another. Special devices have already made available to place on the roofs of houses and flats to (1)_________ the sun’s rays. Thousands of these devices are now being used to (2) _________ power in homes throughout the United States while more than a million solar water - heating units have already been built in (3)_________ in Japan, other purposes for which solar energy is at present being used include the separation of salt (4)_________ seawater. For most people In developing countries, the (5) _________ is not for air conditioners or central heating but for the cheap ways of cooking food, drying crops, and (6)_________ homes.