Acoupleofweeksago，mydadhadatotalkneereplacementoperationonhisleftknee．Laterinhisward，hewaslaughingashetoldthestoryofhearingthehammerandsaw （锯） astheytookoutthebone．Withasmileonhisface，headvisedthedoctorstosharpenthesaw，sincehecouldsmelltheboneburningastheyremovedit．
Hecamehomeanddidtheexercisesthedoctorshadgivenhimandevenwhenithurthemanagedtomakejokesaboutthenewmetalkneebeingheavier，whichmadeithardertolift，buthedidlift，bendandmoveitanyway．
Yesterday，IwenttovisitmyparentsandwastoldbyMomthathewasintheroomforkeepinghistools．Iwalkedintotheroomtofindhimsittingonthebenchlaughing．Iaskedwhatonearthhewasdoing．Heexplainedthatsincesomethingwentwrongwithhiswalker （助行架） hewaschangingthelegsofit．ItseemedthatMom'swalker，whichshehadusedfiveyearsago，wasbrokenonthetop，butthelegswereingoodcondition．Thoselegswouldn'tfitandhecouldn'tgetofftheonehehadchangedsohecouldn'tgetback．
Together，mydad，withtheuselessknee，andI，withthecrippled （残废的） armsandhands，workedandworkedlaughingallthewhile．Themoretroublewehad，theharderwelaughed．Wedidfinallygetthewalkerfixedandgotback．Tiredandfeelingthephysicalpain，wehadcreatedawonderfulheart-warmingmemory．Ihavebeenfortunateenoughtohavemanysuchminuteswithmydad．
21．WhichofthefollowingcanNOTdescribethecharacteroftheauthor'sfather？___
A．Humorous． B．Stubborn．
C．Optimistic． D．Strong-willed．
22．Accordingtothepassagewecaninferthat___．
A．thethreepeopleinthefamilyallhavephysicalproblems．
B．thefathercomplainedaboutthepainindoingtheexercises．
C．themotherrefusedtoofferhelptothefatherintrouble．
D．theauthordoesn'tlikejokingwithpeople．
23．Whichcanbeasuitabletitleforthetext？___
A．MyDad'sKnee
B．LaughingwithMyDad
C．BeingDisabled
D．WalkerinNeed．
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