Jenks, Ernest E.
Alexander hamilton Institute, 1962
Buku Teks SO
Kirkpatrick, Charles A.
South-Western Publishing, 1976
Buku Teks SO
Baduara, Sotar
Akademika Pressindo, 1984
Buku Teks
Baduara, Sotar
Akademika Pressindo, 1984
Buku Teks
Manus-Hannaford, R.G.
Macdonald, 1964
Buku Teks SO