Harre, R.
Littlefield, Adams, 1972
Buku Teks
Colmer, John, author
Methuen, 1984
Buku Teks
O`grady, John, author
Ure Smith, 1973
Buku Referensi
Brown, Robert R.
Aldine Pub. Co., 1963
Buku Teks
editor, Cynthia Macdonald and Garaham Macdonald
Blackwell Publishers, Ltd., 1995
Buku Teks