John B. Calhoun did a classic series of experiments to determine the effects of overpopulation on communities of rats in the 1960s. In each of these experiments, an equal number of male and female adult rats were placed in an enclosure and given an adequate supply of food, water and other necessities. He allowed the rat populations to increase to approximately twice the number that could live in the enclosure without experiencing stress due to overcrowding. He then carefully observed and recorded behavior in these overpopulations communities. At the end of these experiments, Calhoun was able to conclude that overcrowding caused a breakdown in the normal social relationships among rats.
The females, the most seriously affected by the high population density, showed deviant, pathological maternal behavior: they did not behave as mother rats normally do. For example, mothers sometimes abandoned their pops, and, without their mothers' care, the pops died. Under normal conditions, a mother rat would not leave her pops alone to die. The dominant male, the least affected by overpopulation, 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. They did behave pathologically at times. Their antisocial behavior consisted of attacks on weaker male, female, and immature rats. Nondominant males in the experiments also exhibited deviant social behavior. Some withdrew completely; they moved very little and ate and drank at times when the other rats were sleeping in order to avoid contact with them. Other nondominant males were hyperactive, chasing other rats and fighting each other. This segment of the rat population, like all the other parts, was affected by the overpopulation.
【題組】Which of the following statements can be inferred from the passage?
(A)Mother rats usually take care of the pops.
(B)Calhoun had experimented with rats before.
(C)The rats in the experiments have deviant behavior because they fought for necessities of life.
(D)Calhoun manipulated the experiment so that the only factor that caused stress is overpopulation.
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