Ashton, Gail
Routledge, 2000
Buku Teks
Heale, Martin, author
Oxford University Press, 2016
eBooks
Campbell, B. M. S., author.
Cambridge University Press , 2016
Buku Teks
Oxford University Press , 1988
Buku Teks
Peter Brown, editor
Blackwell Publishing, 2007
Buku Teks