bbbb bibb bibi bibo bio- bioi biot biou birb biri biro birr birt biru bito bitt bitu bobb bobi bobo bobu boi- boii boit boiu boob boor boot bor- bori boro borr bort boru botb boti boto bott bour bout brio brit brob broo bror brot brou brrr brut btob btor btrt bttb bubb bubi bubo bubu buir buit buiu bur- burb buri buro burr burt buru but- buti buto butt ibot ibri ibro ibtb iiii iiio iiit iioi iioo iitr iitt iobi ioii ioio ioit iooi iooo iori ioto iri- irio irob irri irti itoi itoo itor itou itri itto itur iuiu obbo obit oboi obor obot obri obro oiii oirt oiti oobi oooo oort ootb orbb orbi orbo orbu ori- orio orit oro- oror orot orri orro orto orub otit oto- otoo otor otro otti otto ottu otur ouii ouir ouit our- ouro ourt out- outb outi outo ouu- rbbb rbbr rib- ribo ribu riot riou riri riti rito ritt ritu rob- robb robi robo robt robu roio roir roit roiu roob rooi roor root rori roro rort roru roti roto rotr rott roub rout rrrr rubb rubi rubu ruit ruri ruro ruru ruti ruto rutt rutu tbit tbrb tibi tibu tiit tiiu tiou tirb tiri tiro tirr tiru titi tito titt titu tobi tobo tobt tobu toit toor toot tori toro torr tort toru toti toto totr tott toui tour tout tri- trib trio trit troi troo trot trou trtr trub trut truu ttbb tttt tubb tubo tubr tubu tuit tuiu tuor turb turi turo turr turt turu tuti tuto tutt tutu tuuo ubbi ubbo ubii ubir ubit uirr uor- urbi urib uriu uro- uroo urri urur urut utor utri utti utto uttu uuri uuuu