common background common bacteria common bacterial common barriers common base common basic common basic principles common basis common bathroom common behavior common behaviors common belief common beliefs common benefit common benefits common bile duct common bird common birds common birth common black common block common blood common blue common board common body common bond common bonds common border common borders common brand common brands common breakfast common browsers common budget common building common bus common business common but differentiated common but differentiated responsibilities common but not common cancer common cancers common car common carotid common carotid artery common carp common carrier common carriers common case common cases common catalogue common categories common category common cathode common cause common cause of blindness common cause of death common causes common causes include common center common central common centre common challenge common challenges common channel common character common characteristic common characteristics common charge common chemical common chemicals common child common childhood common chinese common choice common choices common chronic common citizen common class common classes common classification common clinical common clock common code common cognitive common cold common cold and flu common colds common color common colors common colour common combination common command common commands common commercial common commercial policy common commitment common common common communication