Artikel Jurnal
Marland, Sidney P., author
McGraw-Hill, 1974
Buku Teks
edited by Judith B. Balderston and Frederick E. Balderston
University of California, 1993
Buku Teks
Open University Press, 2003
Buku Teks
Liow, Joseph Chinyong, author
Cambridge University Press, 2009
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