In 1961, scientist set up gigantic, sensitive instruments to collect radio waves from the far reaches of space, hoping to discover in them some mathematical pattern indicating that the waves were sent out by other intelligent beings. The first attempt failed, but someday the experiment may succeed.
　　What reason is there to think that we may actually detect intelligent life in outer space？To begin with, modern theories of the development of stars suggest that almost every star has some sort of family of planets. So any star like our own sun （and there are billions of such stars in the universe） is likely to have a planet situated at such a distance that it would receive about the same amount of radiation as the earth.
　　Furthermore, such a planet would probably have the same general composition as our planet; so, allowing a billion years or two or three, there would be a very good chance for life to develop, if current theories of the origin of life are correct.
　　But intelligent life？Life that has reached the stage of being able to send radio waves out into space in a deliberate pattern？Our own planet may have been in existence for five billion years and may have had life on it for two billion, but it is only in the last fifty years that intelligent life capable of sending radio waves into space has lived on earth. From this it might seem that even if there were no technical problems involved, the chance of receiving signals from any particular earth-type planet would be extremely small.
　　This does not mean that intelligent life at our level does not exist somewhere. There are such an unimaginable number of stars that, even at such miserable possibility, it seems certain that there are millions of intelligent life forms scattered through space. The only trouble is, none may be within easy distance of us. Perhaps none ever will be; perhaps the distances that separate us from our fellow “creatures” of this universe will forever remain too great to be conquered. And yet it is conceivable that someday we may come across one of them or, frighteningly, one of them may come across us. What would they be like, these outside-the-earth creatures？
1.What point is the author making by stating that almost every star has some sort of family of planets？
　　A. Sooner or later intelligent beings will be found on one of the stars.
　　B. There must be one or two of the planets on which there are no intelligent beings.
　　C. There are sufficient planets for there to be one that enjoys the same conditions as the earth does.
　　D. One or two billion years later intelligent beings will generate on those planets.
2.What is the main topic of the passage？
　　A. Some probable intelligent life forms on other planets.
　　B. Various stages undergone by the intelligent life on other planets.
　　C. Grounds for probable existence of intelligent life on other planets.
　　D. The possibility of intelligent life existing on our planet.
3.Which of the following can be inferred from the passage？
A. An encounter is probable between people from the earth and intelligent beings from another planet.
B. Though the first attempt failed, scientists did discover the radio waves sent out by other intelligent beings.
C. Other intelligent beings were able to send our radio waves into space well before the last fifty years.
D. It is certain that there are millions of intelligent beings scattered in space but only too far away.
4.According to the author, what is the difference between “we may come across one of them” and “one of them may come across us”？
A. The earth would be dangerously disadvantaged if it is sought after by possibly much more developed creatures.
B. It would prove that there are too many outside-the-earth creatures if “one of them comes across us”.
C. The history of the development of the earth would be proved to be shorter than that of “them” if “they” come across us.
D. it would prove that the distance in between is not so great as we think if “we come across one of them” someday.