Gre阅读真题200篇 brief contents

Since the Hawaiian Islands have never

There is some dispute about the method of transport involved. Some biologists argue that ocean and air currents are responsible for the transport of plant seeds to Hawaii. Yet the results of flotation experiments and the low temperatures of air currents cast doubt on these hypotheses. More probable is bird transport, either externally, by accidental attachment of the seeds to feathers, or internally, by the swallowing of fruit and subsequent excretion of the seeds. While it is likely that fewer varieties of plant seeds have reached Hawaii externally than internally, more varieties are known to be adapted to external than to internal transport.

17. The author of the passage is primarily concerned with

(A) discussing different approaches biologists have taken to testing theories about the distribution of plants in Hawaii

(B) discussing different theories about the transport of plant seeds to Hawaii

(C) discussing the extent to which air currents are responsible for the dispersal of plant seeds to Hawaii

(D) resolving a dispute about the adaptability of plant seeds to bird transport（B）

(E) resolving a dispute about the ability of birds to carry plant seeds long distances

18. The author mentions the results of flotation experiments on plant seeds (lines 10-12) most probably in order to

(A) support the claim that the distribution of plants in Hawaii is the result of the long-distance dispersal of seeds

(B) lend credibility to the thesis that air currents provide a method of transport for plant seeds to Hawaii

(C) suggest that the long-distance dispersal of seeds is a process that requires long periods of time

(D) challenge the claim that ocean currents are responsible for the transport of plant seeds to Hawaii（D）

(E) refute the claim that Hawaiian flora evolved independently from flora in other parts of the world

19. It can be inferred from information in the passage that the existence in alpine regions of Hawaii of a plant species that also grows in the southwestern United States would justify which of the following conclusions?

(A) The ecology of the southwestern United States is similar in important respects to the ecology of alpine regions of Hawaii.

(B) There are ocean currents that flow from the southwestern United States to Hawaii.

(C) The plant species discovered in Hawaii must have traveled from the southwestern United States only very recently.

(D) The plant species discovered in Hawaii reached there by attaching to the feathers of birds migrating from the southwestern United States.（A）

(E) The plant species discovered in Hawaii is especially well adapted to transport over long distances.

20. The passage supplies information for answering which of the following questions?

(A) Why does successful long-distance dispersal of plant seeds require an equivalence between the ecology of the source area and that of the recipient area?

(B) Why are more varieties of plant seeds adapted to external rather than to internal bird transport?

(C) What varieties of plant seeds are birds that fly long distances most likely to swallow?

(D) What is a reason for accepting the long-distance dispersal of plant seeds as an explanation for the origin of Hawaiian flora?（D）

(E) What evidence do biologists cite to argue that ocean and air currents are responsible for the transport of plant seeds to Hawaii?

30. Viruses, infectious particles consisting

Unfortunately, the common cold (common cold: n. 感冒), produced most often by rhinoviruses, is intractable to antiviral defense. Humans have difficulty resisting colds because rhinoviruses are so diverse, including at least 100 strains. The strains differ most in the molecular structure of the proteins in their capsids. Since disease-fighting antibodies bind to the capsid, an antibody developed to protect against one rhinovirus strain is useless against other strains. Different antibodies must be produced for each strain.

A defense against rhinoviruses might nonetheless succeed by exploiting hidden similarities among the rhinovirus strains. For example, most rhinovirus strains bind to the same kind of molecule (delta-receptors) on a cell’s surface when they attack human cells. Colonno, taking advantage of these common receptors, devised a strategy for blocking the attachment of rhinoviruses to their appropriate receptors. Rather than fruitlessly searching for an antibody that would bind to all rhinoviruses, Colonno realized that an antibody binding to the common receptors of a human cell would prevent rhinoviruses from initiating an infection. Because human cells normally do not develop antibodies to components of their own cells, Colonno injected human cells into mice, which did produce an antibody to the common receptor. In isolated human cells, this antibody proved to be extraordinarily effective at thwarting the rhinovirus. Moreover, when the antibody was given to chimpanzees, it inhibited rhinoviral growth, and in humans it lessened both the severity and duration of cold symptoms.

Another possible defense against rhinoviruses was proposed by Rossman, who described rhinoviruses’ detailed molecular structure. Rossman showed that protein sequences common to all rhinovirus strains lie at the base of a deep “canyon” scoring (score: to mark with lines, grooves, scratches, or notches) each face of the capsid. The narrow opening of this canyon possibly prevents the relatively large antibody molecules from binding to the common sequence, but smaller molecules might reach it. Among these smaller, nonantibody molecules, some might bind to the common sequence, lock the nucleic acid in its coat, and thereby prevent the virus from reproducing.

21. The primary purpose of the passage is to

(A) discuss viral mechanisms and possible ways of circumventing certain kinds of those mechanisms

(B) challenge recent research on how rhinoviruses bind to receptors on the surfaces of cells

(C) suggest future research on rhinoviral growth in chimpanzees

(D) defend a controversial research program whose purpose is to discover the molecular structure of rhinovirus capsids（A）

(E) evaluate a dispute between advocates of two theories about the rhinovirus life cycle

22. It can be inferred from the passage that the protein sequences of the capsid that vary most among strains of rhinovirus are those

(A) at the base of the “canyon”

(B) outside of the “canyon”

(C) responsible for producing nucleic acid

(D) responsible for preventing the formation of delta-receptors（B）

(E) preventing the capsid from releasing its nucleic acid

23. It can be inferred from the passage that a cell lacking delta-receptors will be

(A) unable to prevent the rhinoviral nucleic acid from shedding its capsid

(B) defenseless against most strains of rhinovirus

(C) unable to release the viral progeny it develops after infection

(D) protected from new infections by antibodies to the rhinovirus（E）

(E) resistant to infection by most strains of rhinovirus

24. Which of the following research strategies for developing a defense against the common cold would the author be likely to find most promising?

(A) Continuing to look for a general antirhinoviral antibody

(B) Searching for common cell-surface receptors in humans and mice

(C) Continuing to look for similarities among the various strains of rhinovirus

(D) Discovering how the human body produces antibodies in response to a rhinoviral infection（C）

(E) Determining the detailed molecular structure of the nucleic acid of a rhinovirus

25. It can be inferred from the passage that the purpose of Colonno’s experiments was to determine whether

(A) chimpanzees and humans can both be infected by rhinoviruses

(B) chimpanzees can produce antibodies to human cell-surface receptors

(C) a rhinovirus’ nucleic acid might be locked in its protein coat

(D) binding antibodies to common receptors could produce a possible defense against rhinoviruses（D）

(E) rhinoviruses are vulnerable to human antibodies

26. According to the passage, Rossman’s research suggests that

(A) a defense against rhinoviruses might exploit structural similarities among the strains of rhinovirus

(B) human cells normally do not develop antibodies to components of their own cells

(C) the various strains of rhinovirus differ in their ability to bind to the surface of a host cell

(D) rhinovirus versatility can work to the benefit of researchers trying to find a useful antibody（A）

(E) Colonno’s research findings are probably invalid

27. According to the passage, in order for a given antibody to bind to a given rhinoviral capsid, which of the following must be true?

(A) The capsid must have a deep “canyon” on each of its faces.

(B) The antibody must be specific to the molecular structure of the particular capsid.

(C) The capsid must separate from its nucleic acid before binding to an antibody.

(D) The antibody must bind to a particular cell-surface receptor before it can bind to a rhinovirus.（B）

(E) The antibody must first enter a cell containing the particular rhinovirus.