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  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.
According to the passage, which of the following is a factor that is threatening the survival of coral reef communities?
选项 A、The waters they inhabit contain few nutrient resources.
B、A decline in nutrient input is disrupting their symbiotic relationship with zooxanthellae.
C、The degraded waters of their marine habitats have reduced their ability to carry out photosynthesis.
D、They are too biologically complex to survive in habitats with minimal nutrient input.
E、Waste by-products result in an increase in nutrient input to reef communities.
答案E
解析 哪一个是威胁珊瑚礁群落生存的因素?A．“few nutrient resources”说反了，珊瑚礁就善于在贫营养水体中生存。B．营养减少打乱和动物黄藻的共生关系。无。C．“ability to carry out photosynthesis”文中没说。D．生物上太复杂，不易在贫营养环境中生存。同A，说反了。E．正确。废物副产品导致珊瑚礁群落营养增多。见L23—27。
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