Today, moving and changing are as much a part of a modern business way of life as they are a part of the native American's or the early pioneer's way of life. And the trend is toward even greater mobility, particularly within the management sector of American business. In the early fifties, only eight or nine out of a hundred young men changed their jobs within the first three years with the company. In the past few years, almost thirty-five percent of the college-graduated work force changed jobs within the same period. These people want to intensify their management training. Since most jobs take only a year to a year and a half to master, in order to continue learning, they have to make a job change. Even company presidents tend to be seen as mobile specialists, staying with one company an average of only five years. Company presidents in the United States today tend to be young men who begin their careers with educational backgrounds in engineering science, or business management. They have worked for a few years as technical specialists and quickly moved into higher management positions. Most of them were making ＄ 30 000 per year by the time they reached thirty. On an average, these men have only twenty years working experience at management level when they become company presidents. On the way to the top, they have an average of eleven promotions and seven city transfers. Friendships remain casual and are usually derived from business contracts. Families of these career men have little time to put down roots in and become part of a community. In the past, a few men attained high positions through family and social connections today, high positions go to men who are mobile, and have good educational, backgrounds. According to the passage, an increasing number of future company presidents might be ______.