main requirements main research main research areas main research interest main research interests main researcher main reservoir main residence main residential main resistance main resource main resources main responsibilities main responsibility main responsible main restaurant main result main results main revenue main ridge main riff main rights main ring main risk main risk factor main risk factors main risks main rival main rivals main river main rivers main road main roads main rod main role main roles main roll main roof main room main rooms main root main roster main rotor main round main route main routes main routine main rule main rules main runway main russian main safety main sail main sanctuary main scene main school main schools main science main scientific main screen main seal main seaport main search main season main seasons main seat main secondary main secret main section main sections main sector main sectors main security main segment main segments main selection main selling main selling point main selling points main sensor main sequence main sequence star main series main server main service main services main services provided main session main sessions main set main sets main setting main settings main settlement main settlements main setup main sewer main shaft main share