There have been many great【21】. The first great invention was one that is still very impor

tant to day--the wheel. This made it easier to carry【22】things and to travel long distances.

In the early 1800s the world【23】to change. There was little unknown land left in the world. People did not have to explore much any more. They began to work instead to make life belier.

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 became a big part【24】our life today.

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【25】a new material was first made. Nylon came out in 1935. It changed the kind of clothes people wore.

The middle part of the 20th century brought new ways to help people【26】disease. They worked very well. They made people healthier and let them live【27】lives. 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. Man began【28】ways to go into space. Russia made the first step. Then the United States took a step. Since then other countries, including China and Japan, have made their steps into space.

In 1969 man took his biggest step away from earth. Americans first walked on the moon. This is certainly just a【29】though. New inventions will someday allow us to do things we have never yet【30】.

(56)

A．discoveries

B．creations

C．invention

D．inventions