-er bbb bbe bbk bbo bbr bbs be- beb bee bek beo ber bes bkb bke bkk bko bkr bks bob boe bok boo bor bos brb bre brk bro brr brs bsb bse bsk bso bsr bss ebb ebe ebk ebo ebr ebs eeb eee eek eeo eer ees ekb eke eko ekr eks eo- eob eoe eok eoo eor eos erb ere erk ero err ers es- esb ese esk eso esr ess kbb kbe kbk kbo kbr kbs ke- keb kee kek keo ker kes kkb kke kkk kkr kks kob koe kok koo kor kos krk kro krr krs ksb kse ksk kso ksr kss ob- obb obe obk obo obr obs oeb oee oeo oer oes okb oke okk oko okr oks oo- oob ook ooo oor oos or- orb ore ork oro orr ors os- osb ose osk oso osr oss rbb rbe rbk rbo rbr rbs re- reb ree rek reo rer res rkb rke rkk rko rks rob roe rok roo ror ros rrb rrk rrr rrs rsb rse rsk rso rsr rss sbb sbe sbk sbo sbr sbs se- seb see sek seo ser ses sk- skb ske skk sko skr sks sob soe sok soo sor sos sr- srb sre srk sro srr srs ss- ssb sse ssk sso ssr sss