Moncrieff, A.R. Hope
Gramercy Books, 1995
Buku Referensi
Barnett, Mary
Grange Books, 1997
Buku Referensi
Frost, Frank J.
D.C Heath, 1980
Buku Teks SO
Coleman, Janet
Blackwell Publishers, Ltd, 2000
Buku Teks SO
Martin, Thomas R.
Yale University Press, 1996
Buku Teks SO