参考答案：challenging

解析： 1-20
Everyone experiences stress on some level every day. Stress, broadly defined, is our response to events that we perceive as threatening or challenging. We may experience different levels of stress depending on the stressors, meaning the events or circumstances that cause us to feel stress.
Of course, not everyone perceives the same events or circumstances as stressful; we don’t always react the same way to the same stressors. In fact, something that is extremely stressful for one person may be exciting and non-stressful for another. In general, though, stressful events can be classified into three main categories: cataclysmic events, personal stressors, and background stressors. Cataclysmic events are major events that cause stress suddenly, immediately, for a great many people at once. Examples of these are earthquakes, fires, or other disasters. Personal stressors are major life events that create stress. They can include the death of a loved one, a job loss, a divorce, a financial setback, or a geographical move. They are not always events that we would perceive as negative; many "joyful" life events can also cause a great deal of stress. For example, getting engaged or married, acquiring a new family member (through birth or adoption), starting a new job, and even taking a vacation can all be as stressful as "negative" life events. Finally, background stressors--which we can also think of as day-to-day hassles, or minor irritations--can cause stress, particularly when they add up, when we are repeatedly exposed to them. Examples of background stressors are waiting in a long line, getting stuck in a traffic jam, being exposed to noise, experiencing a delay of some sort, or dealing with broken equipment. Examples of chronic background stressors--and the kind that can lead to long-term health problems--include being unhappy with one’s job, living environment, marriage, or relationship.
Stress is not something that only exists in our mind. Repeated exposure to stressors has both psychological and biological consequences. When we are exposed to stressors, our adrenal glands secrete certain hormones, and our heart rate and blood pressure rise. We experience a "fight or flight" response, a sense of emergency, where the body prepares to defend itself. This is useful in some situations, especially where we might actually need to defend ourselves. In the long run, though, this activation of what is known as the sympathetic nervous system has negative effects and reduces our capacity to manage stress. When stress hormones are constantly secreted, and the body is continually preparing for emergencies, body tissues such as the heart and blood vessels can begin to deteriorate. The immune system functions less effectively, and reduces our ability to fight off illnesses.
The General Adaptation Syndrome, or G. A. S., explains the sequence of physiological reactions to stress. There are three phases to G. A. S. The first is the "alarm and mobilization" phase. This is when we first become aware of a stressor. When we respond with alarm, we may feel upset or confuse& We may even feel a sense of panic or fear. After that, however, we may begin to mobilize our efforts--in other words, to take action to remove the stressor. For example, if you received a mid-semester report stating that your grades were all very low, you might worry at first, but then you would probably make plans to reverse the situation, to improve your grades.
The second phase of G. A. S. is the resistance stage, which occurs if the stressor is not removed. This is the stage when we fight against the stressor or try to cope with the stressor. The attempt to mobilize and remove the source of stress from phase one can result in further stress. For example, if you were studying long hours to try to improve low grades, you might succeed in improving the grades but create more stress in the process.
This can lead to the third G. A. S. phase: exhaustion. In this phose, if resistance was not successful and stressors still exist, our ability to fight or cope with the stressor diminishes. At this point, symptoms of stress manifest themselves psychologically and biologically. Psychologically, we may become irritable, short-tempered, or unable to focus. There may be a sense of being completely overwhelmed and unable to function. Biologically, our bodies may react with such symptoms as aches and pains, fatigue, or illnesses. Interestingly, the exhaustion phase may actually be an extreme way of trying to avoid the stressors. The body may be telling us that we need to take a break, that we need to do whatever is necessary to remove ourselves from the stressor.