Fill in the Blanks cloze-test advancedOnline version Cloze Test C1 by ana mendez 1 history we have wondered about the possibility of life beyond the Earth . It is only in recent years , however , that advances in technology revealed the existence of extrasolar planets ( or " exoplanets " ) , is to say , planets which orbit not our own Sun , but other stars in the universe . So , astronomers have identified a few thousand exoplanets , but believe that billions more exist . Although many astronomers believe that a number of planets in the universe are capable supporting some kind of living organism , or not life has developed on any of them is not yet known . An essential requirement for life is liquid water . If a planet is to have liquid water on its surface , its temperature must be too hot nor too cold . However , such a planet , other the Earth , has yet to be discovered . It may be found in the near future , . Move on to your next mission if you really want to know more .
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