Eastwood, John
Oxford University Press, 1994
Buku Teks
Tomasowa, Francien Herlen
Universitas Brawijaya, 2005
Buku Teks SO
Scobie, Janet I.
George Allen and Unwin, 1959
Buku Teks SO
Howard, Godfrey
Pan Macmillan Publishers, 1993
Buku Referensi
Puchta, Herbert
Cambridge University Press, 2010
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