题目内容：
Questionsarebasedonthefollowingpassage.
Theidealcompanionmachine--thecomputer——wouldnotonlylook,feel,andsoundfriendlybutwouldalsobehaveinapleasantmanner.Itsinformalconversationalstylemakeinteractioncomfortable,andyetthemachinewouldremainslightlyunpredictable(不可预知的)andthereforeveryinteresting.Initsfirstencounteritmightbesomewhathesitant,butasitcametoknowtheuseritwouldprogresstoamorerelaxedandintimatestyle.Themachinewouldnotbeapassiveparticipantbutwouldadditsownsuggestions,information,andopinions;itwouldsometimestaketheinitiativeindevelopingorchangingthetopicandwouldhaveapersonalityofitsown.
Friendshipsarenotmadeinaday,andthecomputerwouldbemoreacceptableasafriendifitimitatedthegradualchangesthatoccurwhenonepersonisgettingtoknowanother.Atanappropriatetimeitmightalsoexpressthekindofaffectionthatstimulatesattachmentandintimacy.Thewholeprocesswouldbeaccomplishedinasubtlewaytoavoidgivinganimpressionofover-familiaritythatwouldbelikelytoproduceirritation(恼怒).Afterexperiencingawealthofpowerful,well-timedfriendshipindicators,theuserwouldbeverylikelytoacceptthecomputerasfarmorethanamachineandmightwellcometoregarditasafriend.
Anartificialrelationshipofthistypewouldprovidemanyofthebenefitsthatpeopleobtainfrominterpersonalfriendships.Thecomputerwouldparticipateininterestingconversationthatcouldcontinuefrompreviousdiscussions.Itwouldhaveafamiliaritywiththeuser'slifeasrevealedinearliercontact,anditwouldbeunderstandingandgood-humored.Thecomputer'sownpersonalitywouldbelivelyandimpressive,anditwoulddevelopinresponsetothatoftheuser.Withfeaturessuchasthese,thecomputermightindeedbecomeaveryattractivesocialpartner.
Whichfeaturebelongstothecomputerasanidealcompanionmachine? A．Cheapinprice.
B．Enjoyableinperformance.
C．Subtleinpersonality.
D．Unpredictableinbehaviour.
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