你的问题中提到的inwhich是属于“介词+关系代词”型的定语从句. 　　关系代词在定语从句中做介词宾语时,从句常由介词+关系代词（只用whom/which）引导 　　Theschool(that/which)heoncestudiedinisveryfamous. 　　=Theschoolinwhichheoncestudiedisveryfamous. 　　TomorrowIwillbringhereamagazine(that/which)youaskedfor. 　　=TomorrowIwillbringhereamagazineforwhichyouasked. 　　We'llgotohearthefamoussinger(whom/that/who)wehaveoftentalkedabout. 　　=We'llgotohearthefamoussingeraboutwhomwehaveoftentalked.