bbbb bftt bobb bobo bobu boff bofu boob boof boor boot bor- borf boro borr bort boru botb boto bott bouf bour bout brfu brob broo bror brot brou brrr brut btob btor btrt bttb bubb bubo bubu buff bufo bufr bur- burb buro burr burt buru but- buto butt ffff ffrr fftf fobt fofo foof foot for- forb foro forr fort foto fott four fout frob frot frou frub ftub fubb fubu fuff fufu fuor fur- furo furr furt futo futu obbo obor obot obro off- offo offr offu ofor ooff oooo oort ootb orbb orbo orbu orff orfu oro- orof oror orot orro orto orub oto- otof otoo otor otro otto ottu otur ouff our- ouro ourt out- outb outo ouu- rbbb rbbr rob- robb robo robt robu roff rofo roob roof roor root roro rort roru roto rotr rott roub rouf rout rrrr rtbf rtfb rubb rubu ruff rufo ruft ruro ruru ruto rutt rutu tbrb tfot tobo tobt tobu toff tofo toft tofu toof toor toot torf toro torr tort toru toto totr tott tour tout trfr troo trot trou trtr trub trut truu ttbb ttff tttt tubb tubo tubr tubu tuff tufo tuft tufu tuor turb turf turo turr turt turu tuto tutt tutu tuuo ubbo ubtf uofo uor- urff urft uro- uroo urur urut utfo utor utto uttu uutf uuuu