A、Space. B、Stress. C、Diet. D、Sleep. A

How much living space does a person need? What happens when his space requirements are not adequately? Sociologists and psychologists are conducting experiments on rats to try to determine the effects of conditions on man. Recent studies have shown that the behavior of rats is greatly affected by space. If rats have adequate living space, they eat well, sleep well, and reproduce well. However, if their living conditions become too crowded, their behavior pattern and even their health change obviously. They cannot sleep and eat well, and signs of fear and tension become obvious. The more crowded they are, the more they tend to bite each other and even kill each other. Thus for rats, population and violence are directly related. Is this a natural law for human society as well? Is adequate space not only desirable, but essential for human survival?
Questions 16 to 18 are based on the passage you have just heard.
16. What affects rats’ behavior?
17. What effect may inadequate living space have on rats according to the passage?
18. What is the experiment done on rats intended to prove?