bbbb bbbs brkb brrr brrs brsb brsr brus bubb bubs bubu bukk buku bur- burb burk burr burs buru busk buss busu buus kbbb kbbk kbbr kbbs kbbu kbkb kbkk kbkr kbrb kbrk kbru kbsb kbsk kbsr kbss kbsu kbub kbuk kbur kbus kbuu kkbb kkbr kkbs kkkk kkrb kkrk kkrr kkrs kksr kkss kksu kkus kkuu krbb krbk krbr krkk krkr krks krku krrb krrk krrr krrs krsk krsr krss krsu kruk krur ksbr ksbs kskb kskk kskr ksks ksku ksrb ksrr ksrs kssr ksss kssu ksub ksuu kubb kubr kubs kubu kukk kuks kuku kurb kurk kurr kurs kuru kusb kusu kuub kuuk kuur kuuu rbbb rbbr rbbs rbss rkss rrrr rubb rubs rubu rukk ruku rurs ruru rusk russ rusu sbbs sbrk sbus skss skur srub ssbr ssrs sssb ssss sub- subb subs suks suku sur- surr surs suru sus- susk suss susu suus ukur urbs urss ursu uruk urur urus us-k usbr usbs ussb ussr usss ussu usus uuuu