Possible Earth﹣Like Planet Next Door？

Scientists say they discovered an earth﹣like planet outside our solar system （太阳系）． It is a planet that could support life．

This planet is just 4.2light years away from us． It is so close that space scientists have considered it as a next door neighbor． They say it could be reached by an unmanned spaceship before the end of the century ﹣﹣ in time for people alive today to see it．

An international team of scientists found the planet moving around the star called "Proxima Centauri"． The result came out last month from the scientific magazine Nature．

Scientists have long thought that a planet with water is important for life． And it has to be neither too hot nor too cold． The newly﹣discovered planet is a little larger than earth Scientists have named it Proxima B． It moves around its sun， Proxima Centauri， once every 11days．

American scientists have been using instruments for years to look for earth﹣like planets． In 2013， scientists' best guess was that there are about one billion （1，000million） "earths" in space．

Alan Boss is the chairman of a group for outer space research． He said that Proxima B not only confirms （确认） the discovery of a planet， but also increases the number of other possible"earths" greatly．

Boss said it is possible， even likely， that most stars have at least one earth﹣like planet， which he considers surprising．

So from the early number of a billion， this new research suggests there may be as many possible earth﹣like planets as there are stars in the Galaxy （银河系）． That is， anywhere from 250billion to 500billion "earths"．

This makes the possibility of living things increasingly likely Boss said he believes human beings will be able to show that there is life in places besides earth in his lifetime． "I am 65，" he said， "but I expect to still be alive when it happens．"

（1）When will it be possible for an unmanned spaceship to reach Proxima B？____

A．	In about eighty years．
B．	In about 4． 2years．
C．	In about eleven days．
D．	In about one billion years．

（2）In the fourth paragraph， the writer thinks that ____ is necessary for life．

A．	water
B．	light
C．	air
D．	wind

（3）What does the underlined word "This" stand for in the last paragraph？____

A．	Scientists have discovered an earth﹣like planet last month．
B．	There are far more earth﹣like planets than people thought．
C．	Proxima B is not far from earth and is just like our neighbor．
D．	The Galaxy will be the only place for living things to live in．

（4）What does Alan Boss mean by saying "but I expect to still be alive when it happens"？　____

A．	His health is in good state and he's sure he will live a long life．
B．	Science is developing much faster than ever in recent years．
C．	Scientists may soon find fact that there's life on other planets．
D．	America is far ahead of other countries in space research．