Respuesta :
Answers: B. The population D. Transportation systems E. Economic production
During these years America was transformed from an underdeveloped nation of farmers into an urbanized economic power station. American society urbanized drastically during this era; millions of people began to move from the farms to the cities. Many other pioneers came from Europe seeking a better life. Also, new models of transportation such as the railroad and the steamboat appeared in this tears as significant changes.