Fromchildhoodtooldage,wealluselanguageasameansofbroadeningourknowledgeofourselvesandtheworldaboutus.Whenhumansfirst1,theywerelikenewbornchildren,unabletousethis2tool.Yetoncelanguagedeveloped,thepossibilitiesforhumankind’sfuture3andculturalgrowthincreased.Manylinguistsbelievethatevolutionis4forourabilitytoproduceanduselanguage.They5thatourhighlyevolvedbrainprovidesus6aninnatelanguageabilitynotfoundinlower7.Proponentsofthisinnatenesstheorysaythatour8forlanguageisinborn,butthatlanguageitselfdevelopsgradually,9afunctionofthegrowthofthebrainduringchildhood.Thereforetherearecritical10timesforlanguagedevelopment.Current11ofinnatenesstheoryaremixed,however,evidencesupportingtheexistenceofsomeinnateabilitiesisundeniable.12,moreandmoreschoolsarediscoveringthatforeignlanguagesarebesttaughtin13grades.Youngchildrenoftencanlearnseverallanguagesbybeing14tothem,whileadultshaveamuchhardertimelearninganotherlanguageoncethe15oftheirfirstlanguagehavebecomefirmlyfixed.16someaspectsoflanguageareundeniablyinnate,languagedoesnotdevelopautomaticallyinavacuum.Childrenwhohavebeen17fromotherhumanbeingsdonotpossesslanguage.Thisdemonstratesthat18withotherhumanbeingsisnecessaryforproperlanguagedevelopment.Somelinguistsbelievethatthisisevenmorebasictohumanlanguage19thananyinnatecapacities.Thesetheoristsviewlanguageasimitative,learnedbehavior.20,childrenlearnlanguagefromtheirparentsbyimitatingthem.Parentsgraduallyshapetheirchild'slanguageskillsbypositivelyreinforcingpreciseimitationsandnegativelyreinforcingimpreciseones.请在18处填上正确答案()
A. exposition
B. comparison
C. contrast
D. interaction