West, Michael D.
Longmans, Green and Co., 1951
Buku Teks SO
Heinemann Educational Books, 1981
Buku Teks SO
French, F. G.
Oxford University Press, 1947
Buku Teks SO
Lambirth, Andrew
Learning Matters, 2005
Buku Teks SO
Tomasowa, Francien Herlen
Universitas Brawijaya , 2005
Buku Teks SO