考博考试

【单选题】What are the chances that we will encounter some alien form of life, as we explore the galaxy.If the argument about the time scale for the appearance of life onEarth is correct, there ought to be many other stars, whose planets have life on them. Some of these stellar systems could have formed 5 billion years before theEarth. So why is the galaxy not crawling with self designing mechanical or biological life forms Why hasn’t theEarth been visied, and even colonizeD、I discount suggestions that UFOs contain beings from outer space. I think any visits by aliens would be much more obvious, and probably also, much more unpleasant.
What is the explanation of why we have not been visited
One possibility is that the argument about the appearance of life onEarth is wrong. Maybe the probability of life spontaneously appearing is so low thatEarth is the only planet in the galaxy, or in the observable universe, in which it happeneD、
Another possibility is that there was a reasonable probability of forming self-reproducing system, like cells, but most of these forms of life did not evolve intelligence.
A、third possibility is that there is a reasonable probability for life to form, and to evolve to intelligent beings, in the external transmission phase.But at that point, the system becomes unstable, and the intelligent life destroys itself. This would be a very pessimistic conclusion. I very much hope it isn’t true.
I prefer a fourth possibility: there are other forms of intelligent life out there, but we have been overlookeD、There used to be a project called SETI, the search for extraterrestrial intelligence. It involved scanning the radio frequencies, to see if we could pick up signals from alien civilizations. I thought this project was worth supporting, though it was cancelled due to a lack of funds.But we should have been wary of answering back, until we have developed a bit further. Meeting a more advanced civilization, at our present stage, might be a bit like the original inhabitants ofAmerica meetingColumbus. I don’t think they were better off for it.
Which of the following is NOT among the four possibilities of why we haven’t been visited ______.
A．Forms of life on the other planets don’t evolve to intelligent beings.
B．Earth is the only planet that contains life in the universe.
C．Life on the other planets destroys itself.
D．Beings from outer space are too far away from us.
网考网参考答案：D
网考网解析：
[解析] 本题的四个选项中，只有D项为正确答案。A、B、C三项都属于作者提到的可能性。 document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>