Freeman, Adam, author
Springer, 2012
eBooks
Backman, Michael
John Wiley & Son, 1999
Buku Teks
Ottaway, J. H.
English Language Book Society and Bailliere Tindall, 1984
Buku Teks
Graham, Wayne, author
Springer, 2012
eBooks
Harryadin Mahardika, author
Universitas Indonesia, 2012
Artikel Jurnal