George, Stephen, author
Oxford University Press, 1985
Buku Teks
Daltrop, Anne, author
Longman, 1982
Buku Teks
Nugent, Neill, author
Macmillan, 1994
Buku Teks
Oxford University Press, 2003
Buku Teks
Wiarda, Howard J., author
Hartcourt College Publishers, 2001
Buku Teks