single point of entry single point of failure single points of failure single pole single police single policy single political single polymer single polypeptide single polypeptide chain single population single port single portal single portion single position single positive single post single pot single pound single power single power supply single precision single premium single press single pressure single price single primary single primer single principle single print single probe single problem single procedure single process single processing single processor single product single production single products single professional single profile single program single programme single programming single programming document single project single promise single propeller single property single protein single proton single prototype single provider single province single public single pulse single pump single punch single purchase single purpose single push single quality single quantum single quarter single queen single question single quotation single quote single quotes single race single rack single radio single rail single rate single ray single reaction single reactor single reading single real single rear single reason single receiver single recipe single recipient single record single recorded single recording single red single red rose single reduction single reference single region single register single registration single relationship single release single released single religion single remote