-er bbb bbe bbo bbr bbt bbx be- beb bee beo ber bet bex bob boe boo bor bot box brb bre bro brr brt brx btb bte bto btr btt btx bxb bxo bxx ebb ebe ebo ebr ebt ebx eeb eee eeo eer eet eex eo- eob eoe eoo eor eot erb ere ero err ert etb ete eto etr ett etx ex- exe exo exr ext exx ob- obb obe obo obr obt obx oeb oee oeo oer oet oex oo- oob ooo oor oot oox or- orb ore oro orr ort orx ot- otb ote oto otr ott ox- oxb oxo oxt oxx rbb rbe rbo rbr rbt rbx re- reb ree reo rer ret rex rob roe roo ror rot rox rrb rrr rrt rtb rte rto rtr rtt rtx rxr t-x tbb tbe tbo tbr tbt te- teb tee teo ter tet tex to- tob toe too tor tot tox trb tre tro trr trt trx ttb tte tto ttr ttt ttx txe txt xbe xbr xbx xee xer xet xex xoo xor xot xox xrt xrx xtr xtx xxo xxx