Câu hỏi:

Read the following text and circle the best answer among A, B, C, or D on your answer sheet for the questions from 39 to 43 

      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 to night, it is hard to slow down. But relaxation is essential for a healthy mind and body. 

      Stress is a natural part of every 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 "fight" or "flight", and in more primitive days the choice made the difference between life or death. The crises we meet today are not likely 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 disease have established links with stress. Since we cannot remove stress from our lives (and it would be unwise to do so even if we could), we need to find ways to deal with it.

In paragraph 3. "such a reaction" refers back to _________