TheAdventuresofTomSawyerand,especially,itssequence()provedthemselvestobethemilestoneintheAmericanliterature.
Thisisanimportantproblem_______toofewsocialscientistshaveresearched.
Therewassomuchnoisethatthespeakercouldn’tmakehimself________.
Itisdifficulttounderstandthiskindof_______calculation.