American social development has been continually beginning over again on the frontier. This perennial rebirth, this fluidity of American life, this expansion westward with its new opportunities, its continuous touch with the simplicity of primitive society, furnish the forces dominating American character.” –Excerpted from The Frontier in American History by Frederick Jackson Turner, 1920 Based on this quotation, one can conclude that Turner believed that the people who most shaped the “American character” were A. pioneers. B. inventors. C. politicians. D. historians.