请问新通用大学英语综合教程第三册unit2textc第四段Hospitalpatientsarepredominantlytheelderlyandtheveryyoung,twocategoriesleastlikelytohaveAIDS.WhydoesMr.Bennettproposetolookthereforthevirusinsteadofamon

　　请问新通用大学英语综合教程第三册unit2textc第四段

　　Hospitalpatientsarepredominantlytheelderlyandtheveryyoung,twocategoriesleastlikelytohaveAIDS.WhydoesMr.Bennettproposetolookthereforthevirusinsteadofamonghigh-riskgroups?Becausehospitalsarewheretestingiseasiest.Sotooarguedthedrunkdriverwholosthiskeysinthedarkandexplainedhewassearchingforthemunderthelamppostbecausethelightwasbetter.

　　还有这段话有哪些主要的语法