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不定项选择题

试题出自试卷《2009年新疆大学考博英语真题及解析》

The word “biodiversity” is a term heard with increasing frequency in the ongoing debate over how best to protect the world’s environment, and more specifically, how to preserve its rapidly dwindling numbers of plant and animal species. In very general terms, “biodiversity” refers to the number of plant and animal species that can be found in a particular habitat or ecosystem. This is apparently a very simple concept, but the simplicity of it belies its significance. A better popular understanding of the real meaning of biodiversity and of its importance to the circumstances in which we presently find ourselves is critical to the success of efforts to protect the environment, and therefore essential to our own survival.
Global biodiversity, which is the total number of plant and animal species existing on the planet at any one time, can only be estimated; and only very roughly estimated at that. Undoubtedly, many species remain to be discovered. Some of these, such as insects and microscopic life, are small enough to have escaped our notice, while others dwell in areas we have only begun to explore; the species inhabiting the deepest ocean depths, for example. It must also be remembered that we are in the midst of a mass extinction event. Species are now disappearing at a rate estimated to be between 1,000 and 10,000 times faster than the average for the history of life on earth. Taken together, these two uncertain elements prevent the global biodiversity estimate from becoming much more than an educated guess. The current best estimate is somewhere in the neighborhood of 100 to 200 million species.
This number, while it may be of some interest to nonscientists, isn’t of much real value to researchers. They are generally more concerned with local biodiversity. Despite the apparent enormity of the number of species that inhabit the earth as a whole, local biodiversity—the number of species found in any one habitat—fluctuates greatly as we cross the boundaries separating the ecosystems that make up the Earth’s biosphere. It reaches its highest levels on the coral reefs and in the tropical rain forests where there may be thousands of species per acre.
Of course, it is this value—the measure of local biodiversity—that is most useful for anyone concerned with assessing the health of an ecosystem or protecting it from destruction. In measuring the biodiversity of a particular ecosystem, biologists are usually quite impartial when weighing the relative significance of each species. Most are assigned a value of one, the total number of species then representing the target value. However, there are two conditions under which one species may be weighted more heavily than others. This would certainly be the case for any species that by virtue of its genetic uniqueness would constitute a special loss to the global gene pool in the event of its extinction. The tuatara is a good example of just such a species. As the only surviving member of a family of reptiles that, except for it, died out 60 million years ago, the tuatara qualifies on grounds of genetic uniqueness to be weighted more heavily in calculating the biodiversity of its habitat.
A species may be accorded bonus points in the biodiversity equation for another reason as well; it may be deemed more significant by virtue of the role it plays in the ecosystem. An example of this would be the California sea otter. [A] The preferred food of this species of marine mammal is the sea urchin; a marine invertebrate, which feeds on a certain type of sea grass known as kelp. [B] Were it not for the otter’s contribution in controlling the sea urchin population, the undersea kelp forest would surely be decimated by a dramatic increase in the population of sea urchins. [C] This would remove a key supporting element—the kelp—from the habitat of many fish and invertebrate species that depend on it. [D] This, in turn, would fundamentally alter an entire undersea habitat and undoubtedly put a risk a number of different species that have adapted to its peculiar characteristics. Therefore, the behavior of the otter in actively maintaining the local diversity of species dictates that it should be assigned a higher biodiversity value.
1. What was the author’s main purpose in writing the passage?
2. It is implied in the passage that we don’t have an accurate measure of global biodiversity because（ ）.
3. The word enormity in the passage is closest in the meaning to（ ）.
4. According to the passage, the largest number of species would be found（ ）.
5. According to the passage, which of the following is NOT important in assessing biodiversity?
6. Which of the following statements is supported by the passage?
7. Look at the four squares marked A, B, C, and D that indicate where the following sentence could be added to the passage.
The effect of this would be a dramatic loss of local biodiversity.
Where would the sentence best fit (A, B, C or D)?
8. Which of the sentences below best expresses the essential information in the italicized sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

问题1选项
A.To explain why biodiversity is essential to our survival.
B.To explain the concept of biodiversity.
C.To show why local biodiversity is more important than global biodiversity.
D.To clarify the dangers that result from declining biodiversity.
问题2选项
A.the number of species is constantly changing
B.populations of animals move from place to place
C.we don’t know the ecological role played by all species
D.the definition of biodiversity is not clear enough
问题3选项
A.important
B.quality
C.vastness
D.accuracy
问题4选项
A.on the coral reefs
B.in the boundary areas between local ecosystems
C.in the undersea kelp forests
D.in fresh water lakes and streams
问题5选项
A.The special function a particular species plays in an ecosystem.
B.The number of species present in an ecosystem.
C.The genetic uniqueness of the species within an ecosystem.
D.The size of the area an ecosystem covers.
问题6选项
A.Local biodiversity may change, but global biodiversity does not.
B.All species have the same significance when considering biodiversity.
C.The concept of biodiversity is of little value to ecologists.
D.The earth is experiencing a reduction in global biodiversity.
问题7选项
A.A
B.B
C.C
D.D
问题8选项
A.As the last of a 60 million year old family of reptiles to die out, the tuatara was so genetically special that it would have raised the calculated biodiversity value of the habitat in which it lived.
B.The tuatara deserves a heavier biodiversity weighting by virtue of the fact that all other genetically similar animals vanished 60 million years ago and therefore, it adds an unusual amount to the local biodiversity value.
C.The tuatara s genetic uniqueness makes it more likely to die out like the other members of its family which disappeared 60 million years ago, and therefore it should be given a higher biodiversity value.
D.Because of the higher biodiversity value contributed by the tuatara to its habitat, the tuatara qualifies for special status to prevent it from vanishing like the other members of its family did 60 million years ago.
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