Ramsay, James W.
Prentice Hall Regents, 1986
Buku Teks
Seal, Bernard, author
Cambridge , 1999
Buku Referensi
Priestley, Philip
Tavistock Publications, 1983
Buku Teks
Haarman, Louann, author
Oxford University Press, 1989
Buku Teks
Langan, John, 1942-, author
McGraw-Hill, 1992
Buku Teks