Carolyn Jackson, Claire Thurgate
McGraw-Hill, 2011
Buku Teks
British Council, 1991
Buku Referensi
Galloway, David, author
Longman, 1987
Buku Teks
Scales, Peter, 1949-, author
Open University Press, 2013
Buku Teks
Scott, Ronaldo Mota David, author
Elsevier, 2014
eBooks