bbb bbi bbo bbr bbs bi- bib bii bio bir bis bob boi boo bor bos brb bri bro brr brs bsb bsi bso bsr bss ibb ibi ibo ibr ibs iib iii iio iir iis io- iob ioi ioo ior ios ir- irb iri iro irr irs is- isb isi iso isr iss o-i ob- obb obi obo obr obs oib oii oio oir ois oo- oob ooi ooo oor oos or- orb ori oro orr ors os- osb osi oso osr oss rbb rbi rbo rbr rbs rib rii rio rir ris rob roi roo ror ros rrb rri rrr rrs rsb rsi rso rsr rss sbb sbi sbo sbr sbs sib sii sio sir sis sob soi soo sor sos sr- srb sri sro srr srs ss- ssb ssi sso ssr sss