Passage 56
Although numbers of animals in a given region may
fluctuate from year to year, the fluctuations are often
temporary and, over long periods, trivial. Scientists
have advanced three theories of population control to
(5) account for this relative constancy.
The first theory attributes a relatively constant popu-
lation to periodic climatic catastrophes that decimate
populations with such frequency as to prevent them
from exceeding some particular limit. In the case of
(10) small organisms with short life cycles, climatic changes
need not be catastrophic: normal seasonal changes in
photoperiod (daily amount of sunlight), for example,
can govern population growth. This theory---the
density-independent view---asserts that climatic factors
(15) exert the same regulatory effect on population regard-
less of the number of individuals in a region.
A second theory argues that population growth is
primarily density-dependent---that is, the rate of
growth of a population in a region decreases as the
(20) number of animals increases. The mechanisms that
manage regulation may vary. For example, as numbers
increase, the food supply would probably diminish,
which would increase mortality. In addition, as Lotka
and Volterra have shown, predators can find prey more
(25) easily in high-density populations. Other regulators
include physiological control mechanisms: for example.
Christian and Davis have demonstrated how the
crowding that results from a rise in numbers may bring
about hormonal changes in the pituitary and adrenal
(30) glands that in turn may regulate population by lowering
sexual activity and inhibiting sexual maturation. There
is evidence that these effects may persist for three
generations in the absence of the original provocation.
One challenge for density-dependent theorists is to
(35) develop models that would allow the precise prediction
of the effects of crowding.
A third theory, proposed by Wynne-Edwards and
termed “epideictic,” argues that organisms have evolved
a “code”in the form of social or epideictic behavior
(40) displays, such as winter-roosting aggregations or group
vocalizing; such codes provide organisms with infor-
mation on population size in a region so that they can,
if necessary, exercise reproductive restraint. However,
wynne-Edwards’ theory, linking animal social behavior
(45) and population control, has been challenged, with some
justification, by several studies.
第三题答案是A,
3. Which of the following, if true, would best support the
density-dependent theory of population control as it is
described in the passage?---类比题
(A) As the number of foxes in Minnesota decrease, the
growth rate of this population of foxes begins of
increase.---密度理论：种群数量增加，增长就会减慢；反之亦然？即当种群数量减少时，物种增长的速度就会加快？
(B) As the number of woodpeckers in Vermont
decreases, the growth rate of this population of
woodpeckers also begins to decrease.
(C) As the number of prairie dogs in Oklahoma
increases, the growth rate of this population of
prairie dogs also begins to increase.
(D) After the number of beavers in Tennessee decreases,
the number of predators of these beavers begins to
increase.
(E) After the number of eagles in Montana decreases,
the food supply of this population of eagles also
begins to decrease.
问题：选项不是直接与文章内容进行类比，而是用反命题方式来支持文章中的原命题。
原命题与逆否命题可以对等，但原命题可以与否命题对等吗？ | 
