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.
The author refers to " filter-feeding animals"(line 30)in order to
选项 A、provide an example of a characteristic sign of reef deterioration.
B、explain how reef communities acquire sustenance for survival.
C、identify a factor that helps herbivore populations thrive.
D、indicate a cause of decreasing nutrient input in waters that reefs inhabit.
E、identify members of coral reef communities that rely on coral reefs for nutrients.
答案A
解析 作者指出“过滤性捕食动物”是为了：A．正确。给出珊瑚礁衰退的一个例证。文中将这列为几个“symptoms”之一。B．“acquire sustenance”不符原文。C．确定帮助植食性种群生存的因素。无。D．指出一个造成营养输入下降的原因。无。E．确定依靠珊瑚礁获得营养的种群。无。
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