Purpura, James E
Cambridge University Press, 2004
eBooks
Read, John
Cambridge University Press, 2000
Buku Teks
Weigle, Sara Chusing
Cambridge University Press, 2002
Buku Teks
Luoma, Sari
Cambridge University Press, 2007
Buku Teks
Laski, Harold J.
George Allen and Unwin, 1948
Buku Teks