-er bbb bbe bbo bbr bbs bbx be- beb bee beo ber bes bex bob boe boo bor bos box brb bre bro brr brs brx bsb bse bso bsr bss bsx bxb bxo bxx ebb ebe ebo ebr ebs ebx eeb eee eeo eer ees eex eo- eob eoe eoo eor eos erb ere ero err ers es- esb ese eso esr ess esx ex- exe exo exr exs exx ob- obb obe obo obr obs obx oeb oee oeo oer oes oex oo- oob ooo oor oos oox or- orb ore oro orr ors orx os- osb ose oso osr oss osx ox- oxb oxo oxx rbb rbe rbo rbr rbs rbx re- reb ree reo rer res rex rob roe roo ror ros rox rrb rrr rrs rsb rse rso rsr rss rsx rxr rxs sbb sbe sbo sbr sbs sbx se- seb see seo ser ses sex sob soe soo sor sos sox sr- srb sre sro srr srs srx ss- ssb sse sso ssr sss ssx sxs xbe xbr xbx xee xer xes xex xoo xor xos xox xrx xsb xss xxo xxx