Cambridge University Press,
Majalah, Jurnal, Buletin
Singapore : The SEAMEO Regional English Language Centre
Majalah, Jurnal, Buletin
Braunschweig Westermann 1995
Buku Teks
Dieter Lohmar
Springer Science, 2012
eBooks
Nedlands : The University of Western Australia Press
Majalah, Jurnal, Buletin