-er bbb bbc bbe bbk bbo bbr bbs bbt bbx bcb bcc bce bck bco bcr bcs bct bcx be- beb bec bee bek beo ber bes bet bex bkb bkc bke bkk bko bkr bks bkt bkx bob boc boe bok boo bor bos bot box brb bre brk bro brr brs brt brx bsb bsc bse bsk bso bsr bss bst bsx btb btc bte btk bto btr bts btt btx bxb bxo bxx c-- cbb cbc cbe cbk cbo cbr cbs cbt cbx ccb ccc cce cck cco ccr ccs cct ccx ce- ceb cec cee cek ceo cer ces cet cex ckb ckc cko cks ckt ckx co- cob coc coe cok coo cor cos cot cox crb crc cre crk cro crr crs crt crx csb csc cse csk cso csr css cst csx ctb ctc cte ctk cto ctr cts ctt ctx cxc cxk cxo cxr cxs cxt cxx ebb ebc ebe ebk ebo ebr ebs ebt ebx ec- ecb ecc ece eck eco ecr ecs ect ecx eeb eec eee eek eeo eer ees eet eex ekb ekc eke eko ekr eks ekt eo- eob eoc eoe eok eoo eor eos eot erb erc ere erk ero err ers ert es- esb esc ese esk eso esr ess est esx etb etc ete etk eto etr ets ett etx ex- exc exe exo exr exs ext exx k-t kbb kbc kbe kbk kbo kbr kbs kbx kcb kcc kce kck kcr kcs kct kcx ke- keb kec kee kek keo ker kes ket kex kkb kkc kke kkk kkr kks kkt kob koc koe kok koo kor kos kot krc krk kro krr krs krt ksb ksc kse ksk kso ksr kss kst ktb ktc kte ktk kto ktr kts ktt kxo ob- obb obc obe obk obo obr obs obt obx oc- ocb occ ock oco ocr ocs oct ocx oeb oec oee oeo oer oes oet oex okb okc oke okk oko okr oks oo- oob ooc ook ooo oor oos oot oox or- orb orc ore ork oro orr ors ort orx os- osb osc ose osk oso osr oss ost osx ot- otb otc ote otk oto otr ots ott ox- oxb oxc oxo oxt oxx rbb rbc rbe rbk rbo rbr rbs rbt rbx rcb rcc rce rco rcr rcs rct rcx re- reb rec ree rek reo rer res ret rex rkb rkc rke rkk rko rks rkt rob roc roe rok roo ror ros rot rox rrb rrc rrk rrr rrs rrt rsb rsc rse rsk rso rsr rss rst rsx rtb rtc rte rtk rto rtr rts rtt rtx rxr rxs sbb sbc sbe sbk sbo sbr sbs sbt sbx scb scc sce sck sco scr scs sct scx se- seb sec see sek seo ser ses set sex sk- skb skc ske skk sko skr sks skt skx sob soc soe sok soo sor sos sot sox sr- srb src sre srk sro srr srs srt srx ss- ssb ssc sse ssk sso ssr sss sst ssx stb stc ste stk sto str sts stt stx sxc sxs sxt t-x tbb tbc tbe tbk tbo tbr tbs tbt tcb tcc tce tck tco tcr tcs tct tcx te- teb tec tee tek teo ter tes tet tex tkb tkc tke tkk tko tkr tks tkt to- tob toc toe tok too tor tos tot tox trb trc tre trk tro trr trs trt trx tsb tsc tse tsk tso tsr tss tst tsx ttb ttc tte ttk tto ttr tts ttt ttx txe txk txs txt xbc xbe xbr xbx xcb xcr xcx xee xer xes xet xex xkb xke xks xoc xok xoo xor xos xot xox xrc xrt xrx xsb xsc xss xst xtc xtr xts xtx xxo xxx