A、People jump higher. B、Egyptians built pyramids. C、Scientists explore the space. D、Da Vinci made plans for transportation. D细节题

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 competition 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 engineer who made plans for a city with roads under the street for traffic. 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 structure.
    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 accepted 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.
Questions:
26. When people participate in sporting activities, what kind of challenge do they face?
27. Which belongs to social challenge?
28. How do people react to the category of social challenges?