2. 外语
  3. Coral reefs are one of the most fragile, biologically complex, and diverse marine ecosystem on Earth. This ecosystem is one of t

Coral reefs are one of the most fragile, biologically complex, and diverse marine ecosystem on Earth. This ecosystem is one of t

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问题     Coral reefs are one of the most fragile, biologically complex, and diverse marine ecosystem on Earth. This ecosystem is one of the fascinating para- doxes of the biosphere: how do clear, and thus nutrient-poor waters support such prolific and productive communities? Part of the answer lies within the tissues of the corals themselves. Symbi- otic cells of algae known as zooxanthel-lae carry out photosynthesis using the metabolic wastes of the coral thereby producing food tor themselves, for their corals, hosts, and even for other mem- bers of the reef community. This symbiotic process allows organisms in the reef community to use sparse nutrient resources efficiently.
    Unfortunately for coral reefs, how- ever, a variety of human activities are causing worldwide degradation of shallow marine habitats by adding nutrients to the water. Agriculture, slash-and-burn land clearing, sewage disposal and manufacturing that creates waste byproducts all increase nutrient loads in these waters. Typical symptoms of reef decline are destabilized herbivore populations and an increasing abundance of algae and filter-feeding animals. Declines in reef communities are consistent with observations that nutrient input is increasing in direct proportion to growing human populations, thereby threat- ening reef communities sensitive to subtle changes in nutrient input to their waters.
It can be inferred from the passage that the author describes coral reef communities as paradoxical most likely for which of the following reasons?
选项 A、They are thriving even though human activities have depleted the nutrients in their environment.
B、They are able to survive in spite of an over-abundance of algae inhabiting their waters.
C、They are able to survive in an environment with limited food resources.
D、Their metabolic wastes contribute to the degradation of the waters that they inhabit.
E、They are declining even when the water surrounding them remains clear.
答案C
解析 作者为什么说珊瑚礁群落“看似矛盾”?文中L6—8明确指出：贫营养水体支撑大量生物种群。∴C正确，能在食物有限的环境下生存。A、B、D、E皆不合原文叙述。
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