Pattie, David, author
Routledge , 2000
Buku Teks
Worth, Katharine
Macmillan, 1990
Buku Teks
Ulfa Hassan, author
1989
UI - Skripsi (Membership)
Sheehan, Paul, author
Cambridge University Press, 2010
eBooks
Yus Ardian Nur Pramujo, author
Fakultas Ilmu Pengetahuan dan Budaya Universitas Indonesia, 2007
UI - Skripsi (Membership)