A、Intellectual challenge. B、Social challenge. C、Physical challenge. D、Economic challenge. CWhen people participate in sporting a

Human beings enjoy challenges. Many of them like physical challenges. They ask themselves questions like these: How fast can I run ? How high can I climb? How deep can I dive? How far can I swim? How long can I hold my breath? How much can I lift? How high can I jump? Because people enjoy challenges, they like to play sports and watch other people play sports. They like climbing, running, diving, lifting, jumping, and so on. Every four years millions of people all over the world enjoy the international sports competitions called the Olympics.
    There are challenges that are not physical challenges. There are social and intellectual challenges, too. Leonardo Da Vinci, who lived in Italy during the fifteenth century, enjoyed every possible challenge. He was an artist and painted the well-known picture, the Mona Lisa. He was an inventor who invented a device to let people breathe under water. He was a scientist, and he learned a great deal about human anatomy.
    Another kind of challenge faced the Egyptians between 4,000 and 5,000 years ago when they decided to build the first pyramid. They used six million tons of rock. That is enough to build a ten-foot wall around all of France. Four hundred thousand men worked for twenty years to build it.
    So, for thousands of years, people accept challenges. Today we still have many challenges before us. Medical science faces the challenges of conquering the many diseases which still attack human beings. Engineers and planners must build new cities and new kinds of transportation. Scientists must develop new forms of energy. And many of us are interested in the challenge of space. We live in an age of challenge.