London:Mansell,London and New York,1981,
Buku Referensi
Byrne, David, author
Routledge, 1998
Buku Teks
Brown, Gary D., author
McGraw-Hill, [Date of publication not identified]
Buku Teks
Mouton, Jane S., author
Hague, 1968
Buku Teks
[T.t.] [t.p.] 1975
Buku Teks