-er bbb bbe bbk bbo bbr be- beb bee bek beo ber bkb bke bkk bko bkr bob boe bok boo bor brb bre brk bro brr ebb ebe ebk ebo ebr eeb eee eek eeo eer ekb eke eko ekr eo- eob eoe eok eoo eor erb ere erk ero err kbb kbe kbk kbo kbr ke- keb kee kek keo ker kkb kke kkk kkr kob koe kok koo kor krk kro krr ob- obb obe obk obo obr oeb oee oeo oer okb oke okk oko okr oo- oob ook ooo oor or- orb ore ork oro orr rbb rbe rbk rbo rbr re- reb ree rek reo rer rkb rke rkk rko rob roe rok roo ror rrb rrk rrr