A、Improved mental functioning. B、Increased susceptibility to disease. C、Speeding up of blood circulation. D、Reduction of stress-

In many stressful situations, the body’s responses can improve our performance. We become more energetic, more alert, better able to take effective action. But when stress is encountered continually, the body’s reactions are more likely to be harmful than helpful to us. The continual speeding up of bodily reactions and production of stress-related hormones seem to make people more susceptible to heart disease. And stress reactions can reduce the disease-fighting effectiveness of the body’s immune system, thereby increasing susceptibility to illnesses ranging from colds to cancer.
    Stress may also contribute to disease in less direct ways by influencing moods and behaviour. People under stress may become anxious or depressed, and as a result may eat too much or too little, have sleep difficulties or fail to exercise. These behavioural changes may in turn be harmful to the health. In addition, people are more likely to pay attention to certain bodily sensations such as aches and pains when they are under stress and to think that they’re sick. If the person were not under stress, the same bodily sensations might not be perceived as symptoms and the person might continue to feel well. Some researchers have suggested that assuming the role of a sick person is one way in which certain people try to cope with stress. Instead of dealing with the stressful situation directly, these people fall sick. After all, it is often more acceptable in our society to be sick and to seek medical help than it is to admit that one can not cope with the stresses of life.
Questions 16 to 19 are based on the passage you have just heard.
16. What does the speaker say about people who encounter stress once in a while?
17. What does the speaker say frequent stress reactions may lead to?
18. What are people more likely to do when they are under stress?
19. What does the passage mainly talk about?