Sitter, Clara L.
Libraries Unlimited, 1992
Buku Referensi
Kingston, John, author
Longman ; York Press, 1992
Buku Referensi
McGraw-Hill, 1994
Buku Teks
Stiles, Karl A., author
McGraw-Hill, 1968
Buku Referensi
edited by Martyn V. Twigg
Wolfe Publishing, 1989
Buku Referensi