Παραπομπή APA
Covey, S. R. (1989). The seven habits of highly effective people: Restoring the character ethic. London: Simon & Schuster.
Παραπομπή Chicago StyleCovey, Stephen R. The Seven Habits of Highly Effective People: Restoring the Character Ethic. London: Simon & Schuster, 1989.
Παραπομπή MLACovey, Stephen R. The Seven Habits of Highly Effective People: Restoring the Character Ethic. London: Simon & Schuster, 1989.
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