接下来的几天给大家整理了历届gre考试阅读真题及解析，下面这篇是1992年4月gre考试阅读真题SECTION A部分。复习gre考试阅读的时候，gre考生应该以往年的真题为复习材料，从真题中总结阅读规律和特点才是制胜法宝。

　　The 1960’s witnessed two profound social movements: the civil rights movement and the movement protesting the war in Vietnam. Although they overlapped in time, they were largely distinct. For a bri moment in 1967, however, it appeared that the two movements might unite under the leadership of Martin Luther King, Jr.

　　King’s role in the antiwar movement appears to require little explanation, since he was the foremost advocate of nonviolence of his time. But King’s stance on the Vietnam War cannot be explained in terms of pacifism alone. After all, he was something of a latecomer to the antiwar movement, even though by 1965 he was convinced that the role of the United States in the war was indensible. Why then the two years that passed bore he translated his private misgivings into public dissent? Perhaps he believed that he could not criticize American foreign policy without endangering the support for civil rights that he had won from the federal government.

　　17. According to the passage, the delay rerred to in lines 12-15 is perhaps attributable to which of the following?

　　(A) King’s ambivalence concerning the role of the United States in the war in Vietnam

　　(B) King’s attempts to consolidate support for his leadership within the civil rights movement

　　(C) King’s desire to keep the leadership of the civil rights movement distinct from that of the antiwar movement

　　(D) King’s desire to draw support for the civil rights movement from the leadership of the antiwar movement

　　(E) King’s reluctance to jeopardize federal support for the civil rights movement

　　18. The author supports the claim that “King’s stance on the Vietnam War cannot be explained in terms of pacifism alone” (lines 10-12) by implying which of the following?

　　(A) There is little evidence that King was ever a student of pacifist doctrine.

　　(B) King, despite pacifist sympathies, was not convinced that the policy of the federal government in Vietnam was wrong.

　　(C) King’s beli in nonviolence was formulated in terms of domestic policy rather than in terms of international issues.

　　(D) Had King’s actions been based on pacifism alone, he would have joined the antiwar movement earlier than he actually did.

　　(E) Opponents of United States foreign policy within the federal government convinced King of their need for support.

　　19. Which of the following can be inferred from the passage about the movement opposing the war in Vietnam?

　　(A) It preceded the civil rights movement.

　　(B) It began in 1965.

　　(C) It was supported by many who otherwise opposed public dissent.

　　(D) It drew support from most civil rights leaders.

　　(E) It was well underway by 1967.

　　20. Which of the following best describes the passage?

　　(A) It discusses an apparent inconsistency and suggests a reason for it.

　　(B) It outlines a sequence of historical events.

　　(C) It shows why a commonly held view is inaccurate.

　　(D) It evaluates an explanation and finally accepts that explanation.

　　(E) It contrasts two views of an issue.

　　What causes a helix in nature to appear with either a dextral (“right-handed,” or clockwise) twist or a sinistral (“lt-handed,” or counterclockwise) twist is one of the most intriguing puzzles in the science of form. Most spiral-shaped snail species are predominantly dextral. But at one time (at one time: adv.同时, 曾经), handedness (twist direction of the shell) was equally distributed within some snail species that have become predominantly dextral or, in a few species, predominantly sinistral. What mechanisms, control handedness and keep lt-handedness rare?

　　It would seem unlikely that evolution should discriminate against (discriminate against: v.歧视) sinistral snails if sinistral and dextral snails are exact mirror images, for any disadvantage that a sinistral twist in itself could confer on its possessor is almost inconceivable. But lt- and right-handed snails are not actually true mirror images of one another. Their shapes are noticeably different. Sinistral rarity might, then, be a consequence of possible disadvantages conferred by these other concomitant structural features. In addition, perhaps lt- and right-handed snails cannot mate with each other, having incompatible twist directions. Presumably an individual of the rarer form would have relative difficulty in finding a mate of the same hand, thus keeping the rare form rare or creating geographically separated right-and lt-handed populations.

　　But this evolutionary mechanism combining dissymmetry, anatomy, and chance does not provide an adequate explanation of why right-handedness should have become predominant. It does not explain, for example, why the infrequent unions between snails of opposing hands produce fewer offspring of the rarer than the commoner form in species where each parent contributes equally to handedness. Nor does it explain why, in a species where one parent determines handedness, a brood is not exclusively right- or lt-handed when the offspring would have the same genetic predisposition. In the European pond snail Lymnaea peregra, a predominantly dextral species whose handedness is maternally determined, a brood might be expected to be exclusively right or lt-handed—and this often occurs. However, some broods possess a few snails of the opposing hand, and in predominantly sinistral broods, the incidence of dextrality is surprisingly high.

　　Here, the evolutionary theory must der to a theory based on an explicit developmental mechanism that can favor either right or lt-handedness. In the case of (in the case of: adv.在...的情况) Lymnaea peregra, studies indicate that a dextral gene is expressed during egg formation; i.e., bore egg fertilization, the gene produces a protein, found in the cytoplasm of the egg, that controls the pattern of cell division (cell division: n.细胞分裂) and thus handedness. In experiments, an injection of cytoplasm from dextral eggs changes the pattern of sinistral eggs, but an injection from sinistral eggs does not influence dextral eggs. One explanation for the differing fects is that all Lymnaea peregra eggs begin lt-handed but most switch to being right-handed. Thus, the path to a solution to the puzzle of handedness in all snails appears to be as twisted as the helix itself.

　　21. Which of the following would serve as an example of “concomitant structural features” (line 19) that might disadvantage a snail of the rarer form?

　　(A) A shell and body that are an exact mirror image of a snail of the commoner form

　　(B) A smaller population of the snails of the rarer form

　　(C) A chip or fracture in the shell caused by an object falling on it

　　(D) A pattern on the shell that better camouflages it

　　(E) A smaller shell opening that restricts mobility and ingestion relative to that of a snail of the commoner form

　　22. The second paragraph of the passage is primarily concerned with offering possible reasons why

　　(A) it is unlikely that evolutionary mechanisms could discriminate against sinistral snails

　　(B) sinistrality is relatively uncommon among snail species

　　(C) dextral and sinistral populations of a snail species tend to intermingle

　　(D) a theory based on a developmental mechanism inadequately accounts for the predominance of dextrality across snail species

　　(E) dextral snails breed more readily than sinistral snails, even within predominantly sinistral populations

　　23. In describing the “evolutionary mechanism” (line 27), the author mentions which of the following?

　　(A) The favorable conditions for nurturing new offspring

　　(B) The variable environmental conditions that affect survival of adult snails

　　(C) The availability of potential mates for breeding

　　(D) The structural identity of offspring to parents of the same hand

　　(E) The frequency of unions between snails of different species

　　24. According to the passage, which of the following is true of Lymnaea peregra?

　　(A) Handedness within the species was at one time equally distributed between lt and right.

　　(B) Under laboratory conditions, dextral eggs from Lymnaea peregra can be artificially induced to develop into sinistral snails.

　　(C) Broods of Lymnaea peregra are, without variation, exclusively sinistral or dextral.

　　(D) Handedness in Lymnaea peregra offspring is determined by only one of the parents.

　　(E) Geographic factors have played a larger role than has genetics in the evolution of the species.

　　25. The passage implies that in Lymnaea peregra, there will generally be

　　(A) more offspring of the nondominant hand in broods where handedness is determined after, rather than bore, fertilization

　　(B) a sinistral gene that produces a protein in the cytoplasm of the egg cell

　　(C) fewer sinistral offspring in dextral broods than dextral offspring in sinistral broods

　　(D) equal numbers of exclusively lt-and right-handed broods

　　(E) an increasing occurrence of lt-handedness in successive broods

　　26. It can be inferred from the passage that a predominantly sinistral snail species might stay predominantly sinistral for each of the following reasons EXCEPT for

　　(A) a developmental mechanism that affects the cell-division pattern of snails

　　(B) structural features that advantage dextral snails of the species

　　(C) a relatively small number of snails of the same hand for dextral snails of the species to mate with

　　(D) anatomical incompatibility that prevents mating between snails of opposing hands within the species

　　(E) geographic separation of sinistral and dextral populations

　　27. Which of the following accurately describes the relationship between the evolutionary and developmental theories discussed in the passage?

　　(A) Although the two theories reach the same conclusion, each is based on different assumptions.

　　(B) They present contradictory explanations of the same phenomenon.

　　(C) The second theory accounts for certain phenomena that the first cannot explain.

　　(D) The second theory demonstrates why the first is valid only for very unusual, special cases.

　　(E) They are identical and interchangeable in that the second theory merely restates the first in less technical terms.

答案：17-27：EDEAEBCDCBC

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