There have been many great inventions that changed the way we live. The first great invention was one that is still very __21__ today-wheel. This made it easier to carry heavy things and to travel long __22__. For hundreds of years after that there were few inventions that had affected our life as much as the wheel had done. Then in the early 1800's the world started to change. There was little unknown land left in the world. People __23__ explore much any more. They began to work to make life __24__. In the second half of the 19th century many great inventions were made. Among them were the camera, the electric light and the radio. These all __25__ a big part of our life today.