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．