DictationListen to the passage. For questions 21 ~ 25, fill in the blanks with

Dictation
   How much (21)living space does a person need? What happens when his space needs are not met? Scientists are doing experiments on rats to try to determine (22)the effects of overcrowded conditions on man. Recent studies have shown that the behavior of rats is greatly affected by space. If rats have enough living space, they eat well, sleep well and produce their young well. But if their living conditions become (23)too crowded, their behavior and even their health change obviously. They can not sleep and eat well, and signs of fear and worry become clear. The more crowded they are, and more they tend to bite each other and even kill each other. Thus, for rats, population and violence are (24)directly related. Is this a natural law for human society as well? Is enough space not only satisfactory, but necessary for (25)human survival? These are interesting questions.