【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