【ResearchershavediscoveredthefirstEarth-sizedplanet．ItwasfirstmarkedbyscientistsusingNASA'sKeplertelescope（望远镜），soit'scalledKepler-186f．Itliesabout500lightyearsfromEarthandgoesarounditsstar．Theplanetis】

　　ResearchershavediscoveredthefirstEarth-sizedplanet．ItwasfirstmarkedbyscientistsusingNASA'sKeplertelescope（望远镜），soit'scalledKepler-186f．Itliesabout500lightyearsfromEarthandgoesarounditsstar．Theplanetistherightdistancefromitsstarforwater：nottoocloseandnottoofar．Waterisoneimportantconditionthatscientistsguessisnecessaryforlife．Soitcouldhavewaterandpossiblelife．It'scalledatrueEarthcousin．

　　"ThisplanetisanEarthcousin，notanEarthtwin，"saidBarclay，whoisamongateamofscientistsreportingonthediscoveryinthemagazineSciencethisweek．

　　"It'sveryexcitingtofindaplanetsimilartotheEarth，"Barclaysaid．"It'snoteasyworkbecausethingschangeaswegetmoremeasurements．"

　　"It'spossibleforlifetoliveinthisplanet，butthatdoesn'tmeanthereislifeinit．"Barclaysaid．

　　Sofar，scientistshavefoundnearly1，800planetsintheuniverse．

　　"ThepastyearhasseenalotofprogressinthesearchforEarth-likeplanets．Kepler-186fisveryimportantbecauseitisthefirstplanetthatisthesametemperatureandisalmostthesamesizeasEarth，"scientistDavidCharbonneauwroteinanemail．

　　48．Researchershavealreadyfoundabout___planetsnow．

　　A.500

　　B.186

　　C.1800

　　D.1801

　　49．WhichofthefollowingaboutKepler-186fisNOTtrueaccordingtothepassage？___

　　A．Itcouldhavewaterandpossiblelife，soperhapswemightlivethere．

　　B．It'salmostashotasandaslargeasEarth．

　　C．Inthefuture，scientistswillstudytheairofitbytelescope．

　　D．It'sanEarth-likeplanet．

　　50．Wecanprobablyreadthisarticlein___．

　　A．astorybook

　　B．anewspaper

　　C．atextbook

　　D．asportmagazine

　　51．Whatisthebesttitleofthepassage？___

　　A．Spaceresearch．

　　B．Journeytospace．

　　C．IstherewaterandpossiblelifeinKepler-186f？

　　D．Scientistsdiscovermostearth-likeplanet．