Severin, Timothy, author
Knopf, 1968
Buku Teks
Standing, T. G.
Longmans, Green and Co., 1951
Buku Teks
Silver, James W., author
Harcourt Brace&world, 1966
Buku Teks
Suber, Peter
Routledge, 1998
Buku Teks
Dalton, Heather, author
Oxford University Press, 2016
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