Source: https://www.devoir.tn/secondaire/Doc/2-%C3%A8me-ann%C3%A9es/Economie-et-services/Economie/Devoirs/devoir-de-synth%C3%A8se-n%C2%B02/devoir-de-synth%C3%A8se-n%C2%B02--2013-2014(kamel-ajour).pdf