【考研英语句子分析NewEngland'sleadersestablishedthebasicthemesandpreoccupationsofanunfolding,dominantPuritantraditioninAmericanintellectuallife这个句子中preoccupationsofanunfolding那个unfolding后面的逗号是什】

　　考研英语句子分析

　　NewEngland'sleadersestablishedthebasicthemesandpreoccupationsofanunfolding,dominantPuritantraditioninAmericanintellectuallife这个句子中preoccupationsofanunfolding那个unfolding后面的逗号是什么意思,表示什么关系啊!