题目

There was once a young man called Paul in a village in the USA. Paul was very lazy because his father was a rich farmer and he didn’t have to work. Mr Smith, a neighbour of his, was a blacksmith (铁匠). He used to work in his shop all day. Paul spent hours and hours watching how the blacksmith worked every day. “Young man, why don’t you try your hand to make a shoe tack (铁钉), even it is only to pass the time?” said the blacksmith one day, “ Maybe it will be useful to you some day.” Finally, the lazy boy began to have a try. After practicing some times, he became skilled and c14．如表是某生态系统中几种生物体内农药含量的测定结果．这些生物与生物之间有着吃与被吃的关系，请分析回答下列问题：生物种类ABCDE单位体积农药含量（毫克）0.0940.0360.0020.2090.010（1）当人类排放的有毒物质进入生态系统，一些不易分解的有毒物质会通过食物链不断积累，请写出表中的生物构成的食物链：C→E→B→A→D．（2）表中有机物含量最多的生物是C（填代号），它是生态系统中的生产者．（3）生态系统的各种成分并不是一成不变的，不同生物的数量虽然总是不断变化，但是各种生物的数量和所占比例却是相对稳定的．说明生态系统具有一定的自动调节能力，但是这种能力是有一定限度的，如果外界干扰过大，生态系统就有可能遭到破坏．在此生态系统中，如果人为因素导致生物D消失，则A的数量在一段时间内会先增加．