McCall, John
Monarch Press, 1966
Buku Teks
Cambridge University Press , 2012
Buku Teks
Leki, Ilona
Cambridge University Press, 1998
Buku Teks
Meyers, Alan, 1945-, author
Pearson Education, 2014
Buku Teks
Roberts, Edgar V., author
Prentice-Hall, 1977
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