听力原文： There have been many great inventions, things that changed the way we live. The first great invention was one that is still very important today—the wheel. For hundreds of years after that there were few inventions that had as much effect as the wheel. Then in the early 1800's the world started to change. There was little unknown land left in the world. People did not have to explore much anymore. They began to work instead to make life better. In the second half of the 19th century many great inventions were made. Among them were the camera, the electric light and the radio. The first part of the 20th century saw more great inventions. The helicopter in 1909. Movies with sound in 1926. The computer in 1928. And jet planes in 1930. This was also a time when a new material was first made. Nylon came out in 1935. The middle part of the 20th century brought new ways to help people get over disease. By the 1960's most people could expect to live to be at least 60. By this time most people had a very good life. Of course new inventions continued to be made. But man now had a desire to explore again. The world was known to man but the stars were not. Man began looking for ways to go into space. Russia made the first step. Then the United States took a step. This is certainly just a beginning though. New inventions will someday allow us to do things we have never yet dreamed of. When did people stop inventing?