APA
national geographic society, . (2001). Earth & Physical Sciences. new york: Mcgraw - hill.
Chicago
national geographic society, . 2001. Earth & Physical Sciences. new york: Mcgraw - hill.
Harvard
national geographic society, . (2001). Earth & Physical Sciences. new york: Mcgraw - hill.
MLA
national geographic society, . Earth & Physical Sciences. new york: Mcgraw - hill. 2001.
