Robinson, Kate
Open University Press, 1995
Buku Teks SO
Delphin, Patricia
Virgnia Reston publishing 1983 , 1983
Buku Teks SO
Joyce, Rosaleen
McGraw-Hill, 2012
Buku Teks SO
Saul Carkiner, Patti Shank, editor
Pfeiffer , 2008
Buku Teks
editors, Saul Carliner, Patti Shank
Pfeiffer, 2008
Buku Referensi