Textbook Problem

(1) Programs to develop clean energy have seen some early notable successes. (2)The price of solar and wind power have both fallen sharply in recent years. (3) The nation's largest wind farm, sprawling across eastern Oregon, is now open and running, and (4) there is even good news from the natural gas front. (5) The use of natural gas, which is far cleaner than coal, to generate electricity has jumped substantially in the last few years, and (6) thanks to government-sponsored research, energy companies are now able to extract much more gas from a tract of land than once seemed possible.