One of the most important discoveries of the nineteenth century was a method of using natural gas for cooking and heating. Large amounts of natural gas are found in the United States, usually several thousand feet below the surface of the earth. Natural gas is most often found in places where petroleum, the oil from which gasoline is made, is found. Often the natural gas must be removed before the oil itself can be reached. For many years after natural gas was first discovered, it was thought to have no value. Finally, however, people began to understand its uses and to find ways of storing it and of moving it from place to place. Today natural gas is stored in large tanks and used for lighting, cooking, and heating. In many ways natural gas is one of our finest fuels. It can be used for cooking without making room hot. It is cheap and can be moved easily from one place to another through long pipelines, some of which are hundreds of miles in length. 1. This passage as a whole is about ______ A. discoverinh natural gas B. finding petroleum C. using natural gas and petroleum D. natural gas and its use 3. What does the word "it" in the passage refer to ? ( It can be used for cooking without making room hot ) A. natural gas B. electric generator C. pipeline D. tank 4. Which of the following is closet meaning to " discovered"? (For many years after natural gas was first discovered, it was thought to have no value.) A. invented B. found C. used D. stored