【阅读理解Weallknowthatbirdsusetheirfeathers(羽毛)tolinetheirnests．Buthaveyoueverheardofabirdeatingitsownfeathers?Itisabirdwhichlivesinthewateranditiscalledt】

　　阅读理解

　　Weallknowthatbirdsusetheirfeathers(羽毛)tolinetheirnests．Buthaveyoueverheardofabirdeatingitsownfeathers?Itisabirdwhichlivesinthewateranditiscalledthegrebe．Thegrebe'sfeathersaresilkytotouchandareblackorgrayincolor．Itisusually7to10incheslongandhasshortwingsandapointedbill(鸟嘴)．Iteatsitsownfeathersandfeedsthemtotheiryoungonestoo．Anditalwayspreferssoftfeatherswhichitgetsridofthroughouttheyear．

　　Scientistsbelievethatitsfeather-eatinghabitislinkedtotheprocessinwhichitthrowswaste．Thegrebehasauniqueexcretorysystem．Itthrowsoutoneortwoballsofwastethroughitsmoutheverytwodays．Themainfoodofgrebeisfish．Sotheballofwastehassomethinghardtodigest(消化)likefishbonesandscales(鱼鳞)．Andthereareparasites(寄生虫)．Itisimportantforthegrebetothrowtheseparasitesout．Ifitdidn'ttheywouldmakeitsick．Accordingtoscientiststhefeathersaddfibertoitswaste．Itmakesiteasiertoform(形成)theballofwasteandtothrowitout．

　　Anotherinterestingcharacteristicisitstoes(脚趾)．Theyareunitedtoformawebnearthebasewhiletherestareroundedlikeanumbrella．Theshapeofitstoeshelpsittoswim．Infactthegrebesareexcellentswimmersandtheyusetheirfeetonlyfordivingforceunderwater．

　　Thegrebemakesitsnestonfloatingleavesorplantsandlaysabouttwototeneggsinit．Boththemaleandfemalegrebehatch(孵化)theeggsandtakecareoftheyoungones．Theyounggrebeshavestripes(条纹)onthem．

　　Thereare18to20speciesofgrebeslivingaroundtheworldsomeofwhichareendangered．

　　(1)

　　Whatdoweknowaboutthegrebe?

　　[]A．

　　Itsfeathersfeelsmooth．

　　B．

　　Ithaswingsabout7to10incheslong．

　　C．

　　Ithasstripesonthebodywhenitgrowsup．

　　D．

　　Onlythemotherg