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达利通留学中介   www.edubridge.com.cn   2017-04-05   来源:达利通留学



  Biologists have long debated about whether egg production in birds is biologically highly costly, some theorizing that egg production is energetically or nutritionally demanding. Lack, however, suggested that clutch size--the number of eggs a bird lays per breeding cycle-- is far below the potential limit of egg production. He suggested that clutch size had instead evolved in relation to the number of young that the parents could successfully rear. Subsequently, most studies focused on limitations operating during chick rearing, particularly among altricial species (species in which the parents feed their young in the nest). Lack later recognized that in precocial species (species in which young feed themselves), clutch size might be explained by different factors -- the availability of food for egg-laying females, for example.

  1. The passage suggests that biologists who say egg production in birds is biologically highly costly would agree that clutch size is determined primarily by

  A. The nutritional and energy demands of egg production.

  B. The number of young that the parents can rear successfully.

  C. Reproductive limitations operating during chick rearing.

  D. The availability of food for newly hatched chicks.

  E. The differences between altricial and precocial species.

  答案:A. 解题线索参考第一句话。

  2. Consider each of the choices separately and select all that apply.

  The passage suggests that Lack would agree with which of the following statements about factors affecting clutch size in birds?

  A. In altricial species, clutch size is determined primarily by factors operating after eggs are laid.

  B. In precocial species, clutch size is determined primarily by factors operating after eggs are laid.

  C. In many bird species, clutch size generally remains well below the potential limit of egg production.

  答案: A C.



  In 1995 the Galileo spacecraft captured data about Jupiter's atmosphere--namely, the absence of most of the predicted atmospheric water--that challenged prevailing theories about Jupiter's structure. The unexpectedness of this finding fits a larger pattern in which theories about planetary composition and dynamics have failed to predict the realities discovered through space exploration. Instead of "normal planets" whose composition could be predicted by theory, the planets populating our solar system are unique individuals whose chemical and tectonic identities were created through numerous contingent events. One implication of this is that although the universe undoubtedly holds other planetary systems, the duplication of the sequence that produced our solar system and the development of life on Earth is highly unlikely.

  Recently planetary scientists have suggested that the external preconditions for the development of Earth's biosphere probably included four paramount contingencies. First, a climate conducive to life on Earth depends upon the extraordinarily narrow orbital parameters that define a continuously habitable zone where water can exist in a liquid state. If Earth's orbit were only 5 percent smaller than it is, temperatures during the early stages of Earth's history would have been high enough to vaporize the oceans. If the Earth-Sun distance were as little as 1 percent larger, run away glaciations on Earth about 2 billion years ago would have caused the oceans to freeze and remain frozen to this day.

  Second, Jupiter's enormous mass prevents most Sun-bound comets from penetrating the inner solar system. It has been estimated that without this shield, Earth would have experienced bombardment by comet-sized impactors a thousand times more frequently than has actually been recorded during geological time. Even if Earth's surface were not actually sterilized by this bombardment, it is unlikely that any but the most primitive life-forms could have survived. This suggests that only planetary systems containing both terrestrial planets like Earth and gas giants like Jupiter might be capable of sustaining complex life-forms.

  Third, the gravitational shield of the giant outer planets, while highly efficient, must occasionally fail to protect Earth. Paradoxically, while the temperatures required for liquid water exist only in the inner solar system, the key building blocks of life, including water itself, occur primarily beyond the asteroid belt. Thus the evolution of life has depended on a frequency of cometary impacts sufficient to convey water, as well as carbon and nitrogen, from these distant regions of the solar system to Earth while stopping short of an impact magnitude that would destroy the atmosphere and oceans.

  Finally, Earth's unique and massive satellite, the Moon, plays a crucial role in stabilizing the obliquity of Earth's rotational axis. This obliquity creates the terrestrial seasonality so important to the evolution and diversity of life. Mars, in contrast, has wildly oscillating tilt and chaotic seasonality, while Venus, rotating slowly backward, has virtually no seasonality at all.

  1. The passage is primarily concerned with

  A. Enumerating conditions that may have been necessary for a particular development

  B. Outlining the conditions under which scientists may be able to predict certain events

  C. Explaining how a particular finding affected scientists ' understanding of a phenomenon

  D. Suggesting reasons why a particular outcome was more likely to occur than other possible outcomes

  E. Assessing the relative significance of factors that contributed to a particular occurrence




  2. It can be inferred from the passage that the "planetary scientists" would be most likely to agree with which of the following statements concerning the development of complex life forms on Earth?

  A. It might have occurred earlier in Earth's history if cometary impacts had been less frequent than they were.

  B. It could have occurred if Earth's orbit were 1 percent larger than it is but not if Earth's orbit were 5 percent smaller.

  C. It probably follows a pattern common on other terrestrial planets that occupy planetary systems containing gas giants.

  D. Its dependence on the effect that Jupiter's gravitational shield has on Earth was difficult to recognize prior to 1995.

  E. It has been contingent on conditions elsewhere in Earth's solar system as well as on conditions on Earth itself.



  题干问planetary scientists 最有可能同意哪个观点,而且是与the development of complex life forms on Earth有关,定位至第二段开头处开始阅读,运用排除法得出答案。

  3. The author of the passage most likely mentions Mars' "oscillating tilt" primarily in order to

  A. Provide evidence for a proposition about the potential effects of cometary impacts

  B. Emphasize the absence from our solar system of "normal planets"

  C. Contrast the rotational axis of Mars with that of Venus

  D. Characterize the role of other planets in the solar system in earth's development

  E. Emphasize the importance of the Moon to the development of life on Earth





  Upon maturity, monarch butterflies travel hundreds of miles from their places of origin and lay their eggs on milkweed. The caterpillars that emerge feed on milkweed and absorb the glycosides in milkweed sap. The specific glycosides present in milkweed differ from region to region within the monarch butterfly’s range. Mature butterflies retain the glycosides in a mature monarch butterfly could be used to determine its place of origin.

  Which of the following, if true, most strengthens the argument?

  A. Mature monarch butterflies do not feed on parts of milkweed that contain glycosides.

  B. The glycosides in milkweed sap are slightly toxic to caterpillars of other species.

  C. The vast majority of the monarch butterflies that are laying eggs in a given region will have traveled there from a single region.

  D. There are substances other than glycosides in milkweed sap that accumulate in a monarch caterpillar and are retained in the body of the mature butterfly.

  E. There are certain glycosides that are found in the sap of all milkweeds, no matter where they grow within the monarch butterfly’s range.


  只有C选项是加强了上文的论点。A削弱 B无关 D削弱 E削弱


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