McKeane, Alasdair
Longman, 1994
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Taylor, Alan John Percivale, 1906-1990
London Routledge 2001,
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Wagner, W Wagner, Wilhelm
Cambridge Cambridge University Press 1908
Buku Teks
Longman, [Date of publication not identified]
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Wilkes, Angela
Passport Books, [Date of publication not identified]
Buku Teks SO