byDavidK.SorenbyDavidK.SorenCover,©GettyImages;p.3,©Corbis;p.4,p.5,©LarryEdwards/Zuma/Corbis;p.6,©StapletonCollection/Corbis;p.7,p.9,©PeterArnold,Inc./Alamy;p.8,©TonyFreeman/PhotoEdit;p.10,©WoodfallWildImages/Alamy;p.11,©Bettmann/Corbis;p.12,©J.G.Photography/Alamy;p.13,©GmbH&Co.K.G./Alamy;p.14,(bl)©DesignPicsInc./Alamy,(br)©PCL/Alamy.Copyright©byHarcourt,Inc.Allrightsreserved.Nopartofthispublicationmaybereproducedortransmittedinanyformorbyanymeans,electronicormechanical,includingphotocopy,recording,oranyinformationstorageandretrievalsystem,withoutpermissioninwritingfromthepublisher.RequestsforpermissiontomakecopiesofanypartoftheworkshouldbeaddressedtoSchoolPermissionsandCopyrights,Harcourt,Inc.,6277SeaHarborDrive,Orlando,Florida32887-6777.Fax:407-345-2418.HARCOURTandtheHarcourtLogoaretrademarksofHarcourt,Inc.,registeredintheUnitedStatesofAmericaand/orotherjurisdictions.PrintedinChinaISBN10:0-15-351531-7ISBN13:978-0-15-351531-6OrderingOptionsISBN10:0-15-351214-8(Grade4AdvancedCollection)ISBN13:978-0-15-351214-8(Grade4AdvancedCollection)ISBN10:0-15-358121-2(packageof5)ISBN13:978-0-15-358121-2(packageof5)Ifyouhavereceivedthesematerialsasexaminationcopiesfreeofcharge,HarcourtSchoolPublishersretainstitletothematerialsandtheymaynotberesold.Resaleofexaminationcopiesisstrictlyprohibitedandisillegal.Possessionofthispublicationinprintformatdoesnotentitleuserstoconvertthispublication,oranyportionofit,intoelectronicformat.1234567891098512111009080706Haveyoueverseenagiraffeeatingleavesandaskedyourself,“Whyisthatgiraffe’stonguesopurple?”Haveyoueverwatchedacatarchitsbackandwondered,“Whyisitdoingthat?”Haveyoueverheardadogbarkandwondered,“Whatisittryingtosay?”Ifyouanswered“yes”toanyofthesequestions,thenyouprobablythinklikeascientist.Scientistshavealotofcuriosity.Theywanttounderstandtheworldaroundthemandwhatmakesitwork.Aschildren,youngscientistsmightaskquestionslike,“Whydoesitrain?”Asadults,theywonderaboutthingsthathumansstilldonotunderstand.Theirquestionsm...
