问题 单项选择题

雷达液位计的天线发射出电磁波,这些波经被测对象表面反射后,再被天线接收,电磁波从发射到()与到液面的距离成正比,雷达液位计记录脉冲波经历的时间,而电磁波的传输速度为常数,则可算出液面到雷达天线的距离,从而知道液面的液位。

A.接收的时间

B.接收的距离

C.接收的面积

D.接收的频率

答案

参考答案:A

阅读理解

阅读理解。

     Man has always wanted to fly. Some of the greatest men in history have thought about the problem.

One of these, for example, was the great Italian artist, Leonardo da Vinci. In the sixteenth century he

made designs for machines that could fly. But they were never built.,

     Throughout history, other less famous men have wanted to fly. An example was a man in England

800years ago. He made a pair of wings from chicken feathers. Then he fixed them to his body and

jumped into the air from a tall building. He did not fly very far. He fell to the ground and broke every

bone in his body.

      The first real step took place in France in 1783. Two brothers, the Mongolfiers, made a very large

"hot air balloon". They knew that hot air rises. Why not fill a balloon with it? The balloon was made of

cloth and paper. In September of that year, the King and Queen of France came to see the balloon.

They watched it carry the very first air passengers into the sky. The passengers were a sheep and a

chicken. We do not know how they felt about the trip. But we do know that the trip lasted 8 minutes

and that the animals landed safely. Two months later, two men did the same thing. They rose above

Paris in a balloon of the same kind. Their trip lasted twenty-five minutes and they traveled about 8

kilometers.

1. Leonardo da Vinci        .

A. said that man would fly in the sky one day

B. built a kind of machine which never flew

C. drew many beautiful pictures of the birds

D. made designs of flying machines

2. Eight hundred years ago an Englishman        .

A. made a kind of flying machine  

B. tried to fly with wings made of chicken feathers  

C. wanted to build a kind of balloon  

D. tried to fly on a large bird

3. In fact, the Englishman who tried to fly        .

A. lost his life            

B. flew only 8 minutes  

C. was not wounded      

D. succeeded in flying

4. The very first air passengers in the balloon were       .

A. the King and Queen      

B. two Frenchmen    

C. two animals            

D. the Mongolfiers

填空题