GMAT考试阅读资料(四)c

Passage 20
　　Species interdependence in nature confers manybenefits on the species involved， but it can also become apoint of weakness when one species involved in the rela-tionship is affected² by a catastrophe³. Thus， flowering（5） plant species dependent on insect pollination⁴， as opposedto self-pollination or wind pollination， could be endan-gered when the population of insect-pollinators is depletedby the use of pesticides⁶.
　　In the forests of New Brunswick， for example，（10） various pesticides have been sprayed in the past 25 yearsin efforts to control the spruce budworm， an economi-cally significant pest. Scientists have now investigatedthe effects of the spraying of Matacil， one of the anti-budworm agents that is least toxic⁷ to insect-pollinators.（15） They studied Matacil‘s effects on insect mortality in awide variety of wild insect species and on plant fecun-dity， expressed as the percentage of the total flowers onan individual plant that actually developed fruit andbore seeds. They found that the most pronounced（20） mortality after the spraying of Matacil occurred amongthe smaller bees and one family of flies， insects that wereall important pollinators of numerous species of plantsgrowing beneath the tree canopy⁸ of forests. The fecun-dity of plants in one common indigenous⁹ species， the（25） red-osier dogwood， was significantly reduced in thesprayed areas as compared to that of plants in controlplots where Matacil was not sprayed. This species ishighly dependent on the insect-pollinators most vulner-able to Matacil. The creeping dogwood， a species similar（30） to the red-osier dogwood， but which is pollinated bylarge bees， such as bumblebees， showed no significantdecline in fecundity¹⁰. Since large bees are not affected bythe spraying of Matacil. these results and weight to theargument that spraying where the pollinators are sensi-（35） tive to the pesticide⁵ used decreases plant fecundity.
　　The question of whether the decrease in plant fecun-dity caused by the spraying of pesticides actually causesa decline in the overall population of flowering plantspecies still remains¹¹ unanswered. Plant species dependent（40） solely¹² on seeds for survival or dispersal are obviouslymore vulnerable to any decrease in plant fecundity thatoccurs， whatever its cause. If， on the other hand， vegeta-tive growth and dispersal （by means of shoots or runners）are available as alternative reproductive strategies for a（45） species， then decreases in plant fecundity may be of littleconsequence. The fecundity effects described here arelikely to have the most profound impact on plant specieswith all four of the following characteristics： a short lifespan， a narrow geographic¹³ range， an incapacity for vege-（50） tative propagation， and a dependence¹ on a small numberof insect-pollinator species. Perhaps we should give specialattention to the conservation of such plant species sincethey lack key factors in their defenses against the envi-ronmental disruption caused by pesticide use.

　　1. Which of the following best summarizes the main point　of the passage？
　　　（A） Species interdependence is a point of weakness for some plants， but is generally beneficial to insects involved in pollination.
　　　（B） Efforts to control the spruce budworm have had deleterious effects on the red-osier dogwood.
　　　（C） The used of pesticides may be endangering certain plant species dependent on insects for pollination.
　　　（D） The spraying of pesticides can reduce the fecundity of a plant species， but probably does not affect its overall population stability.
　　　（E） Plant species lacking key factors in their defenses against human environmental disruption will probably become extinct.

　　2. According to the author， a flowering plant species whose　fecundity has declined due to pesticide spraying may　not experience an overall population decline if the plant　species can do which of the following？
　　　（A） Reproduce itself by means of shoots and runners.
　　　（B） Survive to the end of the growing season.
　　　（C） Survive in harsh climates.
　　　（D） Respond to the fecundity decline by producing more flowers.
　　　（E） Attract large insects as pollinators

　　3. The passage suggests that the lack of an observed decline in the fecundity of the creeping dogwood strengthens the researchers conclusions regarding　 pesticide use because the
　　　（A） creeping dogwood its a species that does not resemble other forest plants
　　　（B） creeping dogwood is a species pollinated by a broader range of insect species than are most dogwood species
　　　（C） creeping dogwood grows primarily in regions that were not sprayed with pesticide， and so served as a control for the experiment
　　　（D） creeping dogwood is similar to the red-osier dogwood， but its insect pollinators are known to be insensitive to the pesticide used in the study
　　　（E） geographical¹⁴ range of the creeping dogwood is similar to that of the red-osier dogwood， but the latter species relies less on seeds for reproduction

　　4. The passage suggests that which of the following is true　of the forest regions in New Brunswick sprayed with　most anti-budworm pesticides other than Matacil？
　　　（A） The fecundity of some flowering plants in those regions may have decreased to an even greater degree than in the regions where Matacil is used.
　　　（B） Insect mortality in those regions occurs mostly among the larger species of insects， such as bumblebees.
　　　（C） The number of seeds produced by common plant species in those regions is probably comparable to the number produced where Matacil is sprayed.
　　　（D） Many more plant species have become extinct in　 those regions than in the regions where Matacil is used.
　　　（E） The spruce budworm is under better control in those regions than in the regions where Matacil is sprayed.

　　5. It can be inferred that which of the following is true of　plant fecundity as it is defined in the passage？
　　　（A） A plant‘s fecundity decreases as the percentage of unpollinated flowers on the plant increases
　　　（B） A plant‘s fecundity decreases as the number of flowers produced by the plant decreases.
　　　（C） A plant‘s fecundity increases as the number of flowers produced by the plant increases.
　　　（D） A plant‘s fecundity is usually low if the plant relies on a small number of insect species for pollination.
　　　（E） A plant‘s fecundity is high if the plant can reproduce quickly by means of vegetative growth as well as by the production of seeds.

　　6. It can be inferred from the passage that which of the　following plant species would be LEAST likely to　experience a decrease in fecundity as a result of the　spraying of a pesticide not directly toxic to plants？
　　　（A） A flowering tree pollinated by only a few insect species
　　　（B） A kind of insect-pollinated vine producing few flowers
　　　（C） A wind-pollinated flowering tree that is short-lived
　　　（D） A flowering shrub¹⁵ pollinated by a large number of insect species
　　　（E） A type of wildflower typically pollinated by larger insects

　　7. Which of the following assumptions most probably underlies¹⁶ the author‘s tentative recommendation in lines 51-54？
　　　（A） Human activities that result in environmental disruption should be abandoned.
　　　（B） The use of pesticides is likely to continue into the future.
　　　（C） It is economically beneficial to preserve endan-gered plant species.
　　　（D） Preventing the endangerment of a species is less costly¹⁷ than trying to save an already endangered one.
　　　（E） Conservation efforts aimed at preserving a few well-chosen species are more cost-effective than are broader-based efforts to improve the environment.