Scientists are now looking for cheaper way to use solar energy to heat air and water. Many buildings are using solar energy to heat their water now. Solar unit on the roofs of buildings collect the energy and use it to heat water. Although these units are still very expensive, more and more people are buying solar hot water heaters. Universities and colleges give solar energy courses where students learn to build their own solar collectors. They are also many books that explain the construction of solar collectors. In the future, there will be more and more solar collectors, especially in the sunny desert areas of the world. 46. What are the scientists doing now?_____________________ 47. Are solar units cheap or expensive? ______________________ 48. Where do students learn to build their own solar collectors __________ 49. Do you think solar energy is expensive__________________ 50. Why do(n’t) you think so? _____________________________