As the pace of life continues to increase, we are fast losing the art of relaxation. (1) you are in the habit of rushing through life, being on the go from morning till night, it is hard to (2) down. But relaxation is (3) for a healthy mind and body.Stress is a (4) part of everyday life and there is no way to (5) it. In fact,it is not the bad thing that it is often supposed to be. A (6) amount of stress is important to provide motivation and give (7) to life. It is only when the stress gets out of control (8) it can lead to poor performance and (9) health.The amount of stress a person can bear(10) very much on the individual. Some people are not afraid of stress, and such (11) are obviously chief material for managerial responsibilities. Others lose heart at first (12) of unusual difficulties. When exposed to stress, in (13) form, we react both chemically and physically. In fact we (14) a choice between escape and fight. But in more ancient days they made the (15) between life and death. The crises (危机)we meet today are (16) to be so extreme,but however little the stress,it requires the same response. It is when such a reaction (17) long，through continued exposure to stress，that health becomes (18) ．Such serious conditions as high blood pressure and heart diseases have (19) links with stress． (20) we canno! remove stress from our lives we need to find ways to deal with it．It would be unwise to do so even it we could．So what do you think of stressWhat is your way to deal with it.
第（8）空应选择（）
A．when
B．why
C．that
D．how
黑磷，黑磷比白磷稳定，结构与石墨相似。下列叙述正确的是