Norwich : Edward Arnold, The educationl, academic and medical publishing
Majalah, Jurnal, Buletin
Holschuh, Louis W.
New York St. Martin's Press 1991,
Buku Teks
Harahap, P.R.
Jakarta Praninta Aksara [date of publication not identified],
Buku Teks
Longman Group UK Limited , 1975
Buku Teks
Beijing Beijing Daxue Chubanshe 1997
Buku Referensi