A classic series of experiments to determine the effects of overpopulation on communities of rats was conducted by a psychologist，John Calhoun．In each experiment，an equal number of male and female adult rats were placed in an enclosure（场地）．The rat populations were allowed to increase．Calhoun knew from experience approximately how many rats could live in the enclosures without experiencing stress due to overcrowding．He allowed the population to increase to approximately 
twice this number Then he fixed the population by removing the children that were not dependent on their mothers．At the end of the experiments，Calhoun was able to conclude that overcrowding causes a breakdown in the normal social relationships among rats，a kind of social disease．The rats in the experiments did not follow the same patterns of behavior as rats would in a community without overcrowding．
The females in the rat population were the most seriously affected by the high population density（密度）．For example，mothers sometimes deserted their children，and，without their mothers’care，the children died．The experiments showed that in overpopulated communities，mother rats do not behave normally．Their behavior may be considered diseased and pathological（病理学的）．
T
he leading males in the rat population were the least affected by over population．Each of these strong males claimed an area of the enclosure as his own．Therefore，these individuals did not experience the overcrowding in the same way as the other rats did．．However leading males did behave pathologically at times．
Their antisocial（反社会）behavior consisted of attacks on weaker male，female，and immature rats．This unusual behavior showed tha
t even though the leading males had enough living space，they too were affected by the general overcrowding．
Non-leading males in the experimental rat communities also exhibited unusual social behavior．Some withdrew（缩回） completely ,avoiding contact with other rats．Other non-leading males were too active，chasing other rats and fighting each other．
The behavior of the rat population has similarity in human behavior．People in densely（密） populated areas exhibit unusual behavior similar to that of the rats in Calhoun’s experiments．In large urban areas，such as New York City，London，and Cairo，there are deserted children．There are cruel，powerful individuals，both men and women．There are also people who withdraw and people who become too active．Is the major cause of these disorders（混乱）overpopulation?
Calhoun’s experiments suggest that it might be．In any case，social scientists and city planners have been influenced by the results of this series of experiments．
小题1:Which of the following inferences（推断）can NOT be made from the first paragraph?
A．Overpopulation causes pathological behavior in rat populations．
B．Calhoun had experimented with rats before．
C．Calhoun’s experiment is still considered important today
D．Stress does not occur in rat communities unless there is overcrowding．小题2:The author implies that the behavior of the leading male rats is sometimes similar to that of
A．people who would like to keep to themselves
B．people who abandon their children
C．too active people
D．cruel，powerful people小题3:The main point of this passage is that _______________．
A．although rats are affected by overcrowding，people are not
B．overcrowding may be an important cause of social pathology
C．the social behavior of rats is seriously affected by overcrowding
D．Calhoun's experiments have influenced many people
