What can we infer from the tragic example given in the first paragraph? [br] The

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问题 What can we infer from the tragic example given in the first paragraph? [br] The "hard" detergents caused trouble during the 1950s because ______.

选项 A、they were not made from vegetables
B、there was not much oxygen in them
C、nowhere could they be treated except in the treatment plants at sewage works
D、their elements could not be broken down into various substances of which they were made

答案 D

解析 细节题。参见文章第二段的第二至五句:...contained elements which could not be degraded in the treatment plants sewage works...(“硬”清洁剂含有在污水工厂的处理车间无法分解的成分,使工厂的效率降低了大约30%,所以排人河里的污水仍含有“硬”清洁剂。这些“硬”清洁剂形成泡沫或在河面扩散,大大减少了河水氧气的融人,并毒害鱼类。)由此可见,“硬”清洁剂引起麻烦的根本原因是含有无法分解的成分。
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