Deborin, G., author
Progress Publishers, 1979
Buku Teks
Boothby, William H, author
Cambridge University Press, 2018
eBooks
Duffy, Helen, author
Cambridge University Press, 2005
Buku Teks
Duffy, Helen, author
Cambridge University Press, 2015
Buku Teks
Schmitt, Michael N., author
T.M.C. Asser Press, 2012
eBooks