Longman Community Information
Longman Grup, 1994
Buku Referensi
O`Hara, Robert A.
E & FN Spon, 1991
Buku Teks
Little, Ian M.D.
At the Clarendon Press , 1953
Buku Teks
Spain, Bryan
CRC Press, Taylor & Francis Group, 2009
Buku Teks
Henderson, Paul, author
Routledge, 1996
Buku Teks