Perry, James W.
Wadsworth, 1996
Buku Referensi
Klett, 2006
Buku Referensi
Douglas J. Eder [and others]
McGraw-Hill Higher Education, 2004
Buku Referensi
Maps Com, 2007
Buku Referensi
edited by] Mhairi G. MacDonald and Jayashree Ramasethu
Wolters Kluwer, Lippincott Williams & Wilkins, 2007
Buku Referensi