One of (19) _______ 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 (20) _______ Earth.
For many years after natural gas first discovered, it was thought to have no value. Finally, therefore, people began (21) _______ 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 (22) _______ ways, natural gas is one of our finest (23) _______. It is cheap and can be used for cooking without making the room hot. It can be moved (24) _______ from one place to another through long pipelines, some of which are hundreds of miles in length.
Question 19.