A、They live a happy and healthy life. B、They are famous for their diligence. C、They work hard outdoors in the fields and eat lit

Why do so many people live to a healthy old age in certain parts of the world? What is the secret of their long lives? Three things seem to be very important: fresh air, fresh food and a simple way of life. These people work near their homes in the clean, mountain air, and they do not have to travel long distances to work by car, bus or train. They do not sit all day in busy offices or factories, but work hard outdoors in the fields. They take more exercise and eat less food than people in the cities of the West. The Hunzas of the Himalayas provide a good example of this. For years they did not need policemen, lawyers or doctors. There was no crime, no divorce and not much illness in their society. They were a happy, peaceful people, famous all over India for their long, healthy lives.
19. According to the passage, what are the factors essential to a long life?
20. What do we know about the Hunzas of the Himalayas from the passage?
21. What is the speaker talking about?