for thousands of years, people have accepted challenges in different fields. there are not only physical challenges, but also social and intellectual challenges. some people risk their lives in playing sports to see how well they can do. others try to make and invent something to make life easier. they all enjoy challenges.

　　why do people enjoy these challenges? there are probably many reasons. one is curiosity. the other is the personal feeling of success, of achievement, and nowadays, for some people, it is a business.

　　today, we still have many challengers before us. medical science faces the challenges of conquering many diseases which still attack human beings. engineers and planners must build new cities, design and produce new kinds of transportation. scientists must develop new forms of energy. in short, we live in an age of challenges.