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. 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 stabilized the population by
removing offspring 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. For example, mothers sometimes abandoned their pups,
and, without their mothers’ care, the pups died. The experiments verified that
in overpopulated communities, mother rats do not behave normally. Their behavior
may be considered diseased, pathological (病理学的).
The dominant 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, dominant males did behave
pathologically at times. Their antisocial behavior consisted of attacks on
weaker male, female, and immature rats. This deviant behavior showed that even
though the dominant males had enough living space, they too were affected by the
general overcrowding.
Non-dominant males in the experimental rat communities also exhibited
deviant social behavior. Some withdrew completely, avoiding contact with other
rats. Other non-dominant males were hyperactive, chasing other rats and fighting
each other.
The behavior of the rat population has parallels in human behavior. People
in densely populated areas exhibit deviant 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 abandoned children. There are cruel, powerful individuals,
both men and women. There are also people who withdraw and people who become
hyperactive. Is the principal cause of these disorders overpopulation? Calhoun's
experiments suggest that it might be. In any ease, social scientists and city
planners have been influenced by the results of this series of experiments.
31. Calhoun stabilized the rat population ____.
A) when it was double the number that could live in the enclosure without
stress
B) by removing young rats
C) so that there was a constant number of adult rats in the enclosure
D) All of the above are correct
32. Which of the following inferences can NOT be made from the first
paragraph?
A) Calhoun’s experiment is still considered important today.
B) Overpopulation causes pathological behavior in rat populations.
C) Stress does not occur in rat communities unless there is
overcrowding.
D) Calhoun had experimented with rats before.
33. According to the passage, which of the following is NOT true?
A) Dominant males had adequate living space.
B) Dominant males were not as seriously affected by overcrowding as the
other rats.
C) Dominant males attacked weaker rats.
D) The strongest males are always able to adapt to bad conditions.
34. The author implies that the behavior of the dominant male rats is
sometimes parallel with
that of _____.
A) cruel, powerful people
B) people who abandon their children
C) hyperactive people
D) people who would like to keep to themselves.
35. 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
Passage 4
In the past, concern about a man-made warming of the earth has concentrated
on the Arctic because the Antarctic is much colder and has a much thicker ice
sheet. But the weather experts are now paying more attention to West Antarctic,
which may be affected by only a few degrees of warming: in other words, by a
warming on the scale that will possibly take place in the next fifty years from
the burning of fuels.
Satellite pictures show that large areas of Antarctic ice are already
disappearing. The evidence available suggests that a warming has taken place.
This fits the theory that carbon dioxide warm the earth.
However, most of the fuel is burnt in the northern hemisphere, where
temperatures seem to be falling. Scientists conclude, therefore, that up to now
natural influences on the weather have exceeded those caused by man. The
question is: which natural cause has most effect on the weather?
One possibility is the variable behavior of the sun. astronomers at one
research station have studied the hot spots and “cold” spots (that is, the
relatively less hot spots) on the sun. as the sun rotated, every 27.5 days, it
presents hotter or “colder” faces to the earth, and different aspects to
different parts of the earth. This seems to have a considerable effect on the
distribution of the earth’s atmospheric pressure, and consequently on wind
circulation. The sun is also variable over a long term: its heat output goes up
and down in cycles, the latest trend being downward.
Scientists are now finding mutual relations between models of solar-weather
interactions and the actual climate over many thousands of years, including the
last Ice Age. The problem is that the models are predicting that the world
should be entering a new Ice Age and it is not. One way of solving this
theoretical difficulty is to assume a delay of thousands of years while the
solar effects overcome the inertia of the earth’s climate. If this is right, the
warming effect of carbon dioxide might thus be serving as a useful
counter-balance to the sun’s diminishing heat.
36. Experts used to believe that the chief reason for global warming
is______.
A) that most fuel is consumed in the northern hemisphere
B) human activities
C) natural influences and carbon dioxide
D) the solar energy
37. The article is written to illustrate ______.
A) the greenhouse effect
B) the solar effects on the earth
C) the models of solar-weather interactions
D) the factors responsible for the global climate
38. In spite of the greater consumption of fuel in the northern hemisphere,
temperatures seem to be falling. This is_____.
A) possibly because of the melting of the ice caps in the poles
B) mainly because the levels of carbon dioxide are rising
C) partly due to the variations of the output of solar energy
D) because the sun presents its “colder” face to the earth
39. On the basis of the models, scientists are of the opinion that
______.
A) the climate of the world should be becoming cooler
B) it’ll take thousands of years for the inertia of the earth’s climate to
take effect
C) the man-made warming effect helps to increase the solar effects
D) the new Ice Age will be delayed by the greenhouse effect
40. If the assumption about the delay of a new Ice Age is correct
_______.
A) the increased levels of carbon dioxide will warm up the earth even more
quickly
B) the greenhouse effect will work to the advantage of the earth
C) the best way to overcome the cooling effect will be to burn more
fuels
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