Long, Calvin T., author
Pearson - Addison Wesley, 2009
Buku Teks
Garstens, Helen L., author
Macmillan, 1969
Buku Teks
Allwright, Dick, author
Cambridge University Press, 1991
Buku Teks
Lesley Cooper and Lynne Briggs
Allen & Unwin, 2000
Buku Teks
Beckmann, Sybilla, author
Pearson Addison Wesley, 2008
Buku Teks