Crabb, John H.
Fred B. Rothman and Company, 1982
Buku Teks
Jonckheere, Karel
Lannoo, 1970
Buku Teks
Bruwier, Marinette.
Arcade, 1976
Buku Referensi
Belgian Business Federation, 1974
Buku Teks
Senelle, Robert
Ministry of Foreign affairs, external trade and co, 1972
Buku Teks