edited by Judith B. Balderston and Frederick E. Balderston
University of California, 1993
Buku Teks
Center for International Higher Education Boston Collage,
Majalah, Jurnal, Buletin
UNESCO, 1978
Buku Teks
edited by Maria Slowey, David Watson
Open University Press, 2003
Buku Teks
Mayhew, Lewis B.
Jossey-Bass, 1973
Buku Teks