题目内容：

    "IF ALIENS are so likely， why have we never seen any？" That is the Fermi Paradox（悻论） ﹣ named after Enrico Fermi， a physicist who posed it in 1950．

Fermi's argument ran as follows． The laws of nature supported the appearance of intelligent life on Earth． Those laws are the same throughout the universe． The universe contains zillions of stars and planets． So， even if life is unlikely to arise on any particular astronomical body， the sheer abundance of creation suggests the night sky should be full of alien civilizations． Fermi wondered why aliens had never visited the earth． Today， the paradox is more usually cast in light of the inability of radio﹣telescope searches to detect the equivalent（相等的） of the radio waves that leak from Earth into the universe， and have done for the past century．

Thinking up answers to this apparent contradiction has become something of a scientific parlour（客厅）game． Perhaps life is really very unlikely． Perhaps the priests are right： human beings were put on Earth by some creator God for His own unknown purposes， and the rest of the universe is merely background scenery． Perhaps there are plenty of aliens， but they have decided that discretion is a safer bet than gathering together． Or perhaps galactic（银河的）  society avoids communicating with Earth specifically．  One frightening idea is that technological civilizations destroy themselves before they can make their presence known． They might blow themselves up after inventing nuclear weapons （an invention that， on Earth， Fermi had been part of）， or cook themselves to death by over﹣burning fossil fuels．

In a paper published last month on arXiv， an online repository（文献库） ， a group of three astronomers at Pennsylvania State University have analyzed the history of alien hunting and come to a different conclusion． In effect， they reject one of the paradox' s main theory．  Astronomers have seen no sign of aliens， argue Jason Wright and his colleagues， because they have not been looking hard enough．

1.What is the Fermi Paradox？

A. The law of universe supported the appearance of aliens but we never see any．

B. A theory about whether aliens exist on the earth and why we can't see them．

C. Fermi thought that aliens never existed because it was completely a paradox．

D. Fermi concluded that aliens did exist but they could not be seen by humans．

2.What can we conclude from the second paragraph？

A. The universe doesn't provide the abundance of creation of life．

B. Fermi thought aliens never visited the earth in the history of human．

C. The inability of radio﹣telescope may result in the failure of finding aliens．

D. The civilizations on the earth have been detected by aliens in the universe．

3.What does the word underlined in the third paragraph mean？

A. Getting together．

B. Fighting each other．

C. Hating each other．

D. Living separately．

4.How do Jason Wright and his colleagues find the Fermi Paradox？

A. They firmly believe that it is out of date．

B. They actually doubt the base of the paradox．

C. They want to prove that it is completely right．

D. They conclude that aliens actually never exist．