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  3. On a clear night you can see many stars in the sky. These stars are millions of miles away. Are there living things on any of th

On a clear night you can see many stars in the sky. These stars are millions of miles away. Are there living things on any of th

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问题     On a clear night you can see many stars in the sky. These stars are millions of miles away. Are there living things on any of the stars? People have always thought about this question. They could not find the answer before now. Today scientists know more about space than ever before. Some machines can help them look for the answer.
    How will scientists do this? People can’ t go to the stars. The stars are far away. A person would take hundreds of years to the next star in a spaceship. So scientists are sending out radio signals. These signals travel in space at the speed of light. At that speed, radio signals will take 25 years to reach the next star. The signals ask "Is there anyone out here?". Living things in space must have machines to hear the signals. We will not get an answer to our signals for more than 50 years. However, scientists are already listening. Someone from space may be trying to send signals to us, too.
    Scientists also have sent large telescopes into space. A telescope can make things look larger. The telescopes are going around the earth. They are looking for life on other worlds. In the next few years we may get an answer to the question, "Is there life in space.
Radio signals will take ______ to reach the next star.
选项 A、25 years
B、50 years
C、hundreds of years
D、a few years
答案A
解析 文章第二段指出，无线电信号以光速行驶，即使如此，到达另一个星球也需要用25年的时间。
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