Webb, James
Bantam Books, 1985
Buku Teks SO
Rand McNally and Company.
Rand Mcnally & Company, 2006
Buku Teks
Ingpen, Robert
Dragon`s World, 1994
Buku Referensi
Rolls, Eric
First Publisher, 1984
Buku Teks SO
Dickson, Paul
Facts on file, 1986
Buku Teks SO