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LessonUniformResourceLocators231.Canyoulistsometop-leveldomainnames?2.Whatdoes“www”standfor?Warm-upExercisesURL统

一资源定位器human-readable人们可读的machine-readable机器可读的IP（IP协议）top-level顶级unique独特，唯一left-most最左convert转换WordPreparation

WhenyouusetheWeborsendane-mailmessage,youuseadomainnametodoit.Forexample,theUniformResourceLocator(URL)"http://www.Yiren

.com"(readash-t-t-p-colon-slash-slash(ordoubleslash)-w-w-w-dot-….)containsthedomainnameYiren.com.Sodoesthise-mailaddress:example@Yiren

.com.Everytimeyouuseadomainname,youusetheInternet'sDNSserverstotranslatethehuman-readabledomainnameintothemachine-readableIPaddres

s.Text每次使用域名时，要用Internet的DNS服务器将可读域名变成机器可读的IP地址Top-leveldomainnames,alsocalledfirst-leveldomainnames

,include.COM,.ORG,.NET,.EDUand.GOV.Withineverytop-leveldomainthereisahugelistofsecond-leveldomains.Forexample,inthe.COMfirst-leveldomaint

hereis:YirenYahooMicrosoftEverynameinthe.COMtop-leveldomainmustbeunique.Theleft-mostword,likewww,isthehostnam

e.Itspecifiesthenameofaspecificmachine(withaspecificIPaddress)inadomain.Agivendomaincan,potentially,containmillionsofhostnamesasl

ongastheyarealluniquewithinthatdomain.Text给定域中可能有几百万个主机名，只要它们在域中全部唯一DNSserversacceptrequestsfromprogramsandothernameserverstoconvertdomainnamesintoIP

addresses.Whenarequestcomesin,theDNSservercandooneoffourthingswithit:1.ItcananswertherequestwithanIPaddressbecaus

eitalreadyknowstheIPaddressfortherequesteddomain.2.ItcancontactanotherDNSserverandtrytofindtheIPaddressforthenamerequested.Itmayhavetod

othismultipletimes.Text3.Itcansay,"Idon'tknowtheIPaddressforthedomainyourequested,buthere'stheIPaddressforaDNSserverthatknowsmorethanIdo."4.Itcan

returnanerrormessagebecausetherequesteddomainnameisinvalidordoesnotexist.TextURLInternetprotocol,datatra

nsmissionstandard:thestandardthatcontrolstheroutingandstructureofdatatransmittedovertheInternetInternetaddress:anaddressidentify

ingthelocationofafileontheInternet,consistingoftheprotocol,thecomputeronwhichthefileislocated,andthe

file’slocationonthatcomputer.FullformUniformResourceLocatorKeyTermsIPQuestionsCanyoulistsometop-leveldomainnames?Whatdoes“www”standfor?.Whe

nyouusetheweb,whatdoestheDNSserversdoforyou?WhydoesDNSserverreturnanerrormessage?ExerciseTranslatethefollowingse

ntencesintoChineseWhenyouusetheWeborsendane-mailmessage,youuseadomainnametodoit.Withineverytop-leveldomainthereisahugelistofsecon

d-leveldomains.Everynameinthe.COMtop-leveldomainmustbeunique.Theleft-mostword,likewww,isthehostname.Itspecifiesthenameofas

pecificmachine(withaspecificIPaddress)inadomain.ExerciseSimplewritingPleasedescribewhattheDNSserversdowhenusetheweb.Exercise——THANKY

OU！——