【答案解析】In the U. S. history, successful presidents were good at making full use of the dominant medium of their times. For example, the Founders of the U. S. were eloquent writes in the age of pamphleteering. F. D. Roosevelt restored hope in the time of "the Great Depression" by mastering radio. And John F. Kennedy was the first president elected because of his understanding of television by which he promoted his image.