-er bbb bbe bbo bbr bbs bbt bbx be- beb bee beo ber bes bet bex bob boe boo bor bos bot box brb bre bro brr brs brt brx bsb bse bso bsr bss bst bsx btb bte bto btr bts btt btx bxb bxo bxx ebb ebe ebo ebr ebs ebt ebx eeb eee eeo eer ees eet eex eo- eob eoe eoo eor eos eot erb ere ero err ers ert es- esb ese eso esr ess est esx etb ete eto etr ets ett etx ex- exe exo exr exs ext exx ob- obb obe obo obr obs obt obx oeb oee oeo oer oes oet oex oo- oob ooo oor oos oot oox or- orb ore oro orr ors ort orx os- osb ose oso osr oss ost osx ot- otb ote oto otr ots ott ox- oxb oxo oxt oxx rbb rbe rbo rbr rbs rbt rbx re- reb ree reo rer res ret rex rob roe roo ror ros rot rox rrb rrr rrs rrt rsb rse rso rsr rss rst rsx rtb rte rto rtr rts rtt rtx rxr rxs sbb sbe sbo sbr sbs sbt sbx se- seb see seo ser ses set sex sob soe soo sor sos sot sox sr- srb sre sro srr srs srt srx ss- ssb sse sso ssr sss sst ssx stb ste sto str sts stt stx sxs sxt t-x tbb tbe tbo tbr tbs tbt te- teb tee teo ter tes tet tex to- tob toe too tor tos tot tox trb tre tro trr trs trt trx tsb tse tso tsr tss tst tsx ttb tte tto ttr tts ttt ttx txe txs txt xbe xbr xbx xee xer xes xet xex xoo xor xos xot xox xrt xrx xsb xss xst xtr xts xtx xxo xxx