The passage follows and explores the history and impact of public education in the U.S. This, then, is central to the passage. The passage begins with a history of public education and then goes on to discuss how higher education creates a more aware citizen which is directly related to the well being of a country (this realization led to the establishment of public universities). So, option C best befits the context here. The ideas of options A, B and D are not central to the passage, so they are incorrect.