bbbb bnor bnrr bobb bobo bobu bonn bono bonu boob boon boor bor- born boro borr boru boun bour brno brob bron broo bror brou brrr brun bubb bubo bubu bunb bunn buno bunu buon bur- burb burn buro burr buru nbbo nnnn nobo nobu non- nonn nono nonu noo- noob noon nooo noor nor- norb norn noro norr noun nour nron nunn nuno nuon nurn nurr nuru obbo obon obor obro onno onon onor onur oooo orbb orbo orbu orno oro- oron oror orro orub oun- our- ourn ouro ouu- rbbb rbbr rnbr rob- robb robo robu rono roob roon roor roro roru roub roun rrrr rrun rubb rubu runn runo ruro ruru ruun ubbo ubon unno unon unro uor- uro- uroo urun urur uuno uuuu