Routledge, 2006
eBooks
Vold, George B. (George Bryan), 1896-1967, author
Oxford University Press, 1979
Buku Teks
edited by Mary Bosworth and Carolyn Hoyle
Oxford University Press, 2013
Buku Teks
Petherick, Wayne A., author
Elsevier, 2010
Buku Teks
edited by S. Venugopal Rao
Vikas Pub. House, 1988
Buku Teks