Insisting upon a market orientation within one's firm first occurred during which era in u. s. business history?

Below are the choices that can be found elsewhere:

a.the production era
b. the sales era
c.the reduction era
d. the marketing concept era
e.the societal marketing era

The answer is D. Firms have achieved great success by putting huge effort into implementing themarketing concept, giving their firms what has been called a market orientation.This meansfocusing efforts on continuously collect information about customer needs, sharing it acrossdepartments, and using it to create customer value.