Delair , 1981
Buku Teks
Coni, Nicholas
Oxford University Press , 1992
Buku Teks
Marsh, Nicholas
Higher and Further Education , 1987
Buku Teks
William Allan Neilson, editor in chief; Thomas A. Knott, general editor; Paul W. Carhart, managing editor
Springfield, G & C Merriam Co.
Buku Referensi
Delair Publishing Company, 1981
Buku Referensi