-- Four            yuan.

    There are robots all around us. Some do very 1   jobs like flying planes and driving subway trains. And some do simple jobs.

    When an automatic自动的) washing machine   2 , water goes in. The machine wait until the water is hot  3   washing the clothes. It does this by "feedback(反馈)". Information about what's happening is fed back into the robot to tell it   4  to do next.

    Our eyes, ears and other senses are our feedback. They tell us   5  around us. So robots are like people in   6 ways. They work and they have feedback.

    But   7   robots look like people. Many are hidden away. Robots control the temperature o f our houses, our cookers, our hot water systems.  We can set the controls to the temperature we want. The robot does 8  . Its feedback usually comes from a thermostat（自动调湿器）.

    One kind of thermostat is a strip(细长片) of metal, which bends(弯曲) when it gets hot. At the right temperature, it bends just enough to work a switch. This turns   9 the heat. As the air around it gets 10   , the metal gets straight, and this turns the heat on again.

Which Is More Useful?

    Thomas is in Grade Two now. He goes to school from Monday to Friday. After school he must do some housework. He helps his parents on the farm(农场) on Saturdays and Sundays. So he doesn't have any time to play football in the daytime. He often plays with his friends in the moon(月亮).

    It's five in the afternoon. School is over. Thomas goes home and cooks for his family. After dinner he sees his friend Paul near his house and asks him to play football. The boy looks at the sky and sees the moon. Then he asks, "Which is more useful, the sun or the moon?"

    "I think the moon is," says Thomas. "We need light(光线) in the evening, but we can not see the sun, but the moon!"

-- With pleasure. But you mustn't          it to others.