Robert, Collin
Paris : Harper Collins Publisher, 2000
Buku Referensi
New York : Holt, Rinehart and Winston, 1995,
Buku Teks
Holschuh, Louis W.
New York: St. Martin`s Press, 1991,
Buku Teks
by L.G. Alexander ... [and others]
Longman, 1975
Buku Teks SO
Harahap, P.R.
Jakarta Praninta Aksara [date of publication not identified],
Buku Teks