Brewis, Joanna, author
Routledge, 2000
Buku Teks
Archer, John, author
Cambridge University Press, 2002
Buku Teks
Lips, Hilary M., author
McGraw-Hill, 2008
Buku Teks
editors, Mary Laing, Katy Pilcher and Nicola Smith
Routledge, 2015
Buku Teks
Simamora, Rudi Sansun, author
2007
UI - Skripsi (Membership)