Why does the marketplace of ideas often have a moderating effect on people's opinions? a. those who shop in the marketplace of ideas typically start with moderate viewpoints. b. moderate ideas are always closest to the truth and, therefore, are most successful in the marketplace of ideas. c. given constant exposure to other people's ideas, it is almost impossible for one not to modify one's own viewpoints. d. moderate ideas usually have the best financial backing and the greatest publicity. e. the most popular ideas are usually the most moderate ones?