Hickler, Holly
Allyn and Bacon, 1979
Buku Teks
Routledge in association with the Open University, 2006
Buku Teks
Shidle, Norman G., author
McGraw-Hill, 1951
Buku Teks
Ross, Janet, author
Harper & Row , 1965
Buku Teks
Giuffré, Giulia, author
Allen & Unwin, 1990
Buku Teks