bbbb bibb bibi bibo bio- bioi biou birb biri biro birr biru bobb bobi bobo bobu boi- boii boiu boob boor bor- bori boro borr boru bour brio brob broo bror brou brrr bubb bubi bubo bubu buir buiu bur- burb buri buro burr buru ibri ibro iiii iiio iioi iioo iobi ioii ioio iooi iooo iori iri- irio irob irri iuiu obbo oboi obor obri obro oiii oobi oooo orbb orbi orbo orbu ori- orio oro- oror orri orro orub ouii ouir our- ouro ouu- rbbb rbbr rib- ribo ribu riou riri rob- robb robi robo robu roio roir roiu roob rooi roor rori roro roru roub rrrr rubb rubi rubu ruri ruro ruru ubbi ubbo ubii ubir uirr uor- urbi urib uriu uro- uroo urri urur uuri uuuu