Allen, B.W.
MacMillan Press, 1995
Buku Teks
Lang, Tran Tien, author
John Wiley & Sons, 1987
Buku Teks
Mottershead, Allen
Prentice-Hall, 1990
Buku Teks
Calvert, J.M., author
John Wiley & Sons, 1978
Buku Teks
Hussain, K.M.
Organization for Economic Co-operation and Development , 1976
Buku Teks