UK : The Association of Commonwealth Universities, 1988,
Buku Referensi
Meister, Jeanne C
McGraw-Hill, Inc, 1998
Buku Teks
Stout, Hiram Miller
Oxford University Press, 1953
Buku Teks
Williams, Basil
Oxford University, 1945
Buku Klasik
Kent Ridge Association of Southeast Asian Institute of Higher Learning 1983, 1983
Buku Teks