Kelly, Miles, author
Miley Kelly Publishing, 2010
Buku Teks
Davis, Loyal Edward,.
Saunders, 1964
Buku Teks
Artikel Jurnal
Wagner, Walter F., author
New York: McGraw-Hill, 1978
Buku Teks
edited by Dagobert D. Runes
Littlefield, Adams & Co., 1959
Buku Referensi