52．There have been many great inventions， things that changed the way we live．The first great inventions was one that is still very important today-the wheel（車輪）． This made it easier to carry heavy things and to travel long distances．
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 didn't have to explore much any more． 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 light and the radio． These all became a big part of our life today．
The first part of the 20th century saw more great inventions． Movies with sound in 1926． This was also a time when a new material（材料） was first made． Nylon came out in 1935． It changed the kind of clothes people wear．
The middle part of the 20th century brought new ways to help people get over diseases． They made people healthier and let them live longer lives．
By the 1960s most people had a very good life． Of course new inventions continued to be made． Man began looking for 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 beginning thought． New inventions will some day help us to do things we have never dreamed of．
（1）What could the first great invention help people do at that time？
（2）How long did it take people to invent Nylon after movies with sound were made？
（3）When did most people have a very good life according to the passage？
（4）What was the greatest thing for human beings in 1969？
（5）What is the main idea of the passage？
