阅读理解。
For more than twenty years scientists have been searching for signs of life on other planets. Most of
these searches have been done over the radio. The hope is that someone in outer space may be trying to
get in touch with us. Scientists also have sent radio and television messages on spaceships traveling through space, on the chance that someone may answer such messages.
Scientists are using powerful radio telescopes to listen to signals from about 1, 000 stars, all within 100
light years of the earth. In addition, they will scan the entire sky to "listen" for radio messages from more
distant stars. Using a computer, they will be able to monitor more than eight channels at one time.
Scientists are looking for any signal that stands out from the background noise.
Of the 200 billion stars in the Milky Way galaxy(银河星系), scientists find that 5% are like our sun.
Perhaps half of them have a planet like the earth. Such a planet would be a reasonable distance from the
star for temperatures to be right for the evolution(进化) of life. Based on the inhabitable (适于居住的)
planets in our galaxy, most scientists agree that chances are likely that one or more of these planets
support some life.
However, many scientists wonder whether intelligent life exists on other planets. Some believe that
twenty years of searching without any intelligible messages shows that no one is out there. They say that
the evolution of intelligence comparable to ours is unlikely.
Other scientists believe that our search hasn't been long enough to rule out the possibility that intelligent
life exists in our galaxy. If we hope to find intelligent life, these scientists believe that we have to keep
looking.
1. According to the passage, how many planets in our galaxy might be inhabitable?
A. 5 billion.
B. 10 billion.
C. 15 billion.
D. 200 billion
2. The first paragraph in this passage is mainly about ________ .
A. how scientists are looking for signs of life on other planets
B. why scientists are looking for signs of life on other planets
C. where scientists are looking for signs of life on other planets
D. when scientists are looking for signs of life on other planets
3. The underlined word "monitor" in the 2nd paragraph means " ________ ".
A. find
B. block
C. check
D. form
4. Which of these statements is True based on the information in the passage?
A. The earth is one of the oldest planets in our galaxy.
B. Most scientists believe that there is intelligent life on other planets.
C. Scientists don't believe that there might be life on other planets.
D. Scientists are trying different ways to find signs of life on other planets.