References :

Ausubel, David. Educational Psychology: A Cognitive View. New York: Holt, Rinehartand Wiston, 1968, 1978.

Krashen, Stephen. Principles and Practice in Second Language Acquisition. New York:Pergamon Press, 1982. Terrell, Tracy D. "A Natural Approach to Second Language Acquisition and Learning." Modern Language Journal 61 (1977): 325-237.