2. 外语
  3. The reason for not classifying carbon dioxide as a pollutant is that it is a natural component of the atmosphere and needed by p

The reason for not classifying carbon dioxide as a pollutant is that it is a natural component of the atmosphere and needed by p

admin2012-06-26  73
问题     The reason for not classifying carbon dioxide as a pollutant is that it is a natural component of the atmosphere and needed by plants to carry out biological synthesis. No one would argue that carbon dioxide is a necessary component of the atmosphere any more than one would argue the fact that Vitamin D is necessary in the human diet. However, excess intake of Vitamin D can be extremely toxic. Living systems, be they an ecosystem or an organism, require that a delicate balance be maintained between certain compounds in order for the system to function normally. When the excess presence of one substance threatens the wellbeing of an ecosystem, it becomes toxic despite the fact that it is required in small quantities.
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答案之所以不把二氧化碳列为污染物，是因为二氧化碳是大气的天然成份，植物进行生物合成需要二氧化碳。正如人们普遍认为人的饮食不可缺少维生素D一样，也都认为二氧化碳是大气不可缺少的成份。但是摄入过多的维生素D会有很大的副作用。生命系统，不论是生态系统还是生物，都需要在某些化合物之间保持微妙的平衡，以确保系统功能正常。尽管少量的某种物质是必要的，但当该物质过量出现威胁生态系统的健康时，就具有了毒副作用。
解析     1．第一句的表语从句中有it is a natural component of the atmosphere and needed by plants to carry out biological synthesis，其中it is a...and needed...可理解为needed前面省略了it is，后面的不定式充当目的状语，意义相当于plants need carbon dioxide to carry out biological synthesis。
    2．第二句是该段落中最难理解的句子，难就难在如何理解No one would argue that...any more than one would argue...，字面意思是“一个人为……争辩的力度不会超过……，意译就是“对两者相信的程度相同”。
    3．第四句。Living systems, be they an ecosystem or an organism...就是“不论是生态系统，还是生物(有机体)”。require后的从句是虚拟语气，动词用原形。excess可当形容词用，相当于excessive。名词quantity number和amount可与介词in连用充当状语，如import oil in large quantities(大量进口石油)或kill the enemy in large numbers(消灭大量敌人)。
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