Psychologists once believed that the motive that caused men to strive to attain high-level managerial positions was the "need for achievement". But now they believe it is the "need for power".
Power seekers strive hard to reach positions where they can exercise authority over large numbers of people. (46) Individual performers who lack this drive are not likely to advance far up the managerial ladder. They usually scorn company politics and devote their energies to other types of activities. The power game is part of management, and it is played best by those who enjoy it most.
(47) One of the least rational acts of business organizations is that of hiring managers who have a high need to exercise authority, and then teaching them that authoritative methods are wrong and that they should be consultative or participative. (48) It is a serious mistake to teach managers that they should adopt styles that are inconsistent with their unique personalities. Yet this is precisely what a large number of business organizations are doing; and it explains, in part, why their management development programs are not effective.
(49) What managerial aspirants should be taught is how to exercise their authority in a way that is appropriate to the situation and the people involved. They need to learn that the real source of their power is their own knowledge and skill, and the strength of their own personalities, not the authority conferred on them by their positions. When they lack the knowledge or skill required to perform the work, they need to know how to share their authority. (50) But when they know what has to be done and have the skill and personality to get it done, they must exercise their traditional authority in whatever way is necessary.

一辆汽车以20m/s的速度沿平直的公路从甲地开往乙地，又以30m/s的速度从乙地开往丙地．已知甲、乙两地间的距离与乙、丙两地间的距离相等，该汽车在从甲地开往丙地的过程中平均速度的大小为（）

A．22 m/s

B．24 m/s

C．25m/s

D．28 m/s