Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 19 to 24.

One of ___(1)___ 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 ___(2)___ Earth.
For many years after natural gas first discovered, it was thought to have no value. Finally, therefore, people began ___(3)___ 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 ___(4)___ ways, natural gas is one of our finest ___(5)___. It is cheap and can be used for cooking without making the room hot. It can be moved ___(6)___ from one place to another through long pipelines, some of which are hundreds of miles in length.