Hilt, Rinehart and Winston, 1967
Buku Teks
Gee, Wilson, author
D. Appleton-Century Company, 1934
Buku Teks
Womack, James G., author
Benziger Bros, 1966
Buku Teks
editor, James P. Shaver
Macmillan, 1991
Buku Referensi
edited by R. Meurig Evans
Macmillan, 1975
Buku Teks