The human thirst [for knowledge] / is / driving force [behind our successful development as a species] 主语:the human thirst 定语(或补语):for knowledge 谓语:系动词is,表语driving force 定语(或补语):behind our successful development as a species thirst:作名词,表示“渴望”、“渴求”(感觉这俩词本来不是汉语固有词汇,是源自thirst这个词造出来的)