单项选择题

TEXT A
As the pace of life continues to increase, we are fast losing the art of relaxation. Once you are in the habit of rushing through life, being on the go from morning till night, it is hard to slow down. But relaxation is essential for a healthy mind and body.
Stress is natural part of everyday life and there is no way to avoid it. In fact, it is not the bad thing it is often supposed to be. A certain amount of stress is vital to provide motivation and give purpose to life. It is only when the stress gets out of control that it can lead to poor performance and ill health.
The amount of stress a person can withstand depends very much on the individual. Some people are not afraid of stress, and such characters are obviously prime material for managerial responsibilities. Others lose heart at the first signs of unusual difficulties. When exposed to stress, in whatever form, we react both chemically and physically. In fact we make choice between "flight and fight" and in more primitive days the choices made the difference between life and death. The crises we meet today are unlikely to be so extreme, but however little the stress, it involves the same response. It is when such a reaction lasts long, through continued exposure to stress, that health becomes endangered. Such serious conditions as high blood pressure and heart diseases have established links with stress. Since we cannot remove stress from our lives (it would be unwise to do so even if we could), we need to find ways to deal with it.
According to the author, the most important character for a good manager is his______.