edited by Manfred E. Wolff
John Wiley & Sons, 1995
Buku Teks
John Wiley & Sons, 2002
eBooks
Wilson, 1967-, author
IKIP semarang, 1982
Buku Teks
Jenkins, Glenn L., author
McGraw-Hill, 1953
Buku Teks
KAT International Marketing Service, 1972
Buku Referensi