Galloway, David, author
Longman, 1987
Buku Teks
Scott, Ronaldo Mota David, author
Elsevier, 2014
eBooks
Harrold, Ann
Library Association, 1986
Buku Referensi
Barry Dufour ,Will Curtis
McGraw-Hill, 2011
Buku Teks
Curtis, Audrey, author
Routledge, 2009
Buku Teks