William, Kate
Dian Rakyat, 1995
Buku Teks
William, Kate
N.Y. Bantam Books, 1988
Buku Teks
William, Kate
Bantam Bokks, 1992
Buku Teks
Cohen, William, author
Amacom, American Management Association., 1986
Buku Teks
Kolk, Geert van der, author
Uitgeverij Veen, 1991
Buku Teks