Kotler, P., & Armstrong, G. (2001). Principles of marketing (9th ed.). Prentice Hall.

Kotler, Philip, and Gary Armstrong. Principles of Marketing. 9th ed. Upper Saddle River, N.J. : New Delhi: Prentice Hall, 2001.

Kotler, Philip, and Gary Armstrong. Principles of Marketing. 9th ed. Prentice Hall, 2001.