Tillett, Gregory, author
Routledge & Kegan Paul, 1982
Buku Teks
Frolik, Lawrence A., author
West Publishing , 2010
Buku Teks
Kapp, Marshall B., author
Jones & Bartllett, 2010
Buku Teks
Scott-Kilvert, Ian, author
Longmans, Green, 1970
Buku Teks
Merriam-Webster's, Incorporated, 1993
Buku Referensi