Graver, B.D.
Walton Street , 1987
Buku Teks
Hewings, Martin, author
Cambridge University Press, 2005
Buku Teks
Hewings, Martin, author
Cambridge University Press, 2006
Buku Teks
Dhanny R. Cyssco, author
Puspa Swara, 2004
Buku Teks
Murphy, Raymond, author
Cambridge University Press, 1998
Buku Teks