题目内容：
根据下面内容，回答题 Americaisamobilesociety.FriendshipsbetweenAmericanscanbecloseandreal,yetdisappearsoonifsituationschange.
Neithersidefeelshurtbythis.BothmayexchangeChristmasgreetingsforayearortwo,perhapsafewlettersforawhile--thennomore.Ifthesametwopeoplemeetagainbychance,evenyearslater,theypickupthefriendshipwhereitleftoffandaredelighted.
ThiscanbequitedifficultforusChinesetounderstand,becausefriendshipsbetweenusflowermoreslowlybutthenmaybecomelifelongfeelings,extending(延伸)sometimesdeeplyintobothfamilies.
Americansarereadytoreceiveusforeignersattheirhomes,sharetheirholidays,andtheirhomelife.Theywillenjoywelcomingusandbepleasedifweaccepttheirhospitality(好客)easily.
AnotherdifficultpointforusChinesetounderstandAmericansisthatalthoughtheyincludeuswarmlyintheirpersonaleverydaylives,theydon'tshowtheirpolitenesstousifitrequiresagreatdealoftime.Thisisusuallytheoppositeofthepracticeinourcountrywherewemaybegenerouswithourtime.Sometimes,we,ashosts,willappearatairportseveninthemiddleofthenighttomeetafriend.Wemaytakedaysofftoactasguidestoourforeignfriends.TheAmericans,however,expresstheirwelcomeusuallyathomes,buttrulycannotmanagethetimetodoagreatdealwithavisitoroutsidetheirdailyroutine.Theywillprobablyexpectustogetourselvesfromtheairporttoourownhotelbybus.Andtheyexpectthatwewillphonethemfromthere.Oncewearriveattheirhomes,thewelcomewillbefull,warmandreal.Wewillfindourselvestreatedhospitably.
FortheAmericans,itisoftenconsideredmorefriendlytoinviteafriendtotheirhomesthantogotorestaurants,exceptforpurelybusinessmatters.Soaccepttheirhospitalityathome!
Thewriterofthispassagemustbe__________. A．anAmerican
B．aChinese
C．aprofessor
D．astudent
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答案解析：