The British Council, 2001
Buku Referensi
Levi, Leo
John Wiley & Sons, 1980
Buku Teks
Houghton Miffiln, 1958
Buku Teks
Woodworth, David P
Boston Spa: The British Library Document Supply Centre, 1986
Buku Referensi
Shattock, Joanne
Oxford University Press, 1993
Buku Referensi