单选题
How much living space does a person need? What happens when these space requirements are not adequately met? Sociologists and psychologists are【K17】______experiments on rats to try to determine the effects of【K18】______on humans. Recent studies have shown that the【K19】______ of rats is greatly affected by space. If rats have adequate【K20】______space, they eat well, sleep well, and reproduce well. But, if their living conditions become too crowded, their behavior 【K21】______and even their health conditions【K22】____________perceptibly. They cannot sleep and eat well, and【K23】____________of fear and tension become obvious. The more【K24】____________they are, the more they【K25】____________to bite each other and even【K26】____________each other. Thus, for rats, population and violence are directly【K27】____________. Is this a【K28】____________law for human society as well? Is adequate space not【K29】____________desirable but also【K30】____________for human survival?