c-- ccc ccd cco ccr ccs cdc cdd cdo cdr cds co- coc cod coo cor cos crc crd cro crr crs csc csd cso csr css dcc dcd dco dcr dcs ddc ddd ddo ddr dds doc dod doo dor dos drc drd dro drr drs dsc dsd dso dsr dss oc- occ ocd oco ocr ocs odc odd odo odr ods oo- ooc ood ooo oor oos or- orc ord oro orr ors os- osc osd oso osr oss rcc rcd rco rcr rcs rdc rdd rdo rdr rds roc rod roo ror ros rrc rrd rrr rrs rsc rsd rso rsr rss scc scd sco scr scs sdc sdd sdo sdr sds soc sod soo sor sos sr- src srd sro srr srs ss- ssc ssd sso ssr sss