bbbb bbbs bobb bobo bobs boob boor boos boot bor- boro borr bors bort boso boss bost botb boto bots bott brob broo bror bros brot brrr brrs brsb brsr brst bsos bsts btob btor btrt btss bttb obbo obor obos obot obro obsr obss obst obts oooo ooos oort oost ootb oots orbb orbo orbs oro- oror oros orot orro orrs orso orto orts osoo osor osos osro ossb osso ostr osts otbs oto- otoo otor otos otro otrs otso otto otts rbbb rbbr rbbs rbss rbst rob- robb robo robs robt roob roor roos root roro rort roso ross rost roto rotr rots rott rrrr rsos rsts rtss rtts s-os sbbs sbor sbot sbst sobo sobr sobs sobt soor soos soot sorb soro sorr sors sort soso soss sost soto sots sros srtr ssbr ssot ssrs sssb ssss sstb ssts stbs stob stoo stor stos stot stro strs stss sttr tbbs tbrb tbst tobo tobs tobt toor toos toot toro torr tors tort tosb toso toss tost toto totr tots tott troo tros trot trst trtr tsob tsos tssr tsst tsts ttbb ttss tttt