Johnson, Debra, author
Routledge, Taylor & Francis group, 2003
Buku Teks
O`Hare, Greg, author
Oliver & Boyd, 1988
Buku Teks
Oxford University Press, 1998
Buku Teks
Williams, Edward A.
McGraw-Hill, 1983
Buku Teks
Southall, Ivan, author
Melbourne: Oxford University Press, 1964
Buku Teks