Scheer, James F
Alpha Omega Press, 2002
Buku Teks SO
Scheer, James F
Alpha Omega Press, 2002
Buku Teks SO
Ritchason, Jack
Woodland Health Books, Pleasant Grove, Utah, 1995
Buku Teks SO
Trivedi, A.K
Sahni Publications, 2003
Buku Teks SO
Foster, Steven
National Geographic Society, 2006
Buku Teks SO