Vernon-Wortzel, Heidi
John Wiley & Sons, 1997
Buku Teks
Davenport, Thomas H.
Publicis, 2006
Buku Teks
United Nations Departemen of Public Information, 1990
Buku Teks
Salvatore, Dominick
McGraw-Hill, 1993
Buku Teks
Sachs, Jeffrey D.
Harvester, 1993
Buku Teks