Michael R. Czinkota, Ilkka A. Ronkainen, Michael H. Moffet, Eugene O. Moynihan
Harcourt College publishers, 2001
Buku Teks
Daniels, John L
McGraww-Hill, 1993
Buku Teks
Dunning, John H.
George Allen and Unwin , 1974
Buku Teks
edited by Lorraine Eden
St. Martin's Press, 1993
Buku Teks
Nobes, C.W.
Philip Allan/St. Martin Press, 1988
Buku Teks