Read the passage and fill in the blank with the correct word. We are looking for 27________, clean, and effective sources of energy. These types of energy won't cause pollution or waste natural resources. Solar power is one of these energy sources. It will be provided freely by the sun. One percent of the solar energy that reaches the earth will be enough to provide electricity for the whole 28________of the world. Solar energy will (29) ________by many countries around the world. Solar panels will be put on the roofs 30________houses and other buildings and 31________sun's energy will be used to heat water. The energy will be stored for a long time. We hope that by using solar energy the problem of the energy shortage will be solved. 27. A. cheap B. harmful C. limited D. non – renewable 28. A. populate B. populating C. population D. populated 29. A. be use B. be used C. used D. be uses 30. A. in B. on C. from D. of 31. A. a B. the C. X D. an