The reason for this is easy to recognise: in nature, the existent organisms either adapt or are regularly replaced by new types.
原因很容易理解：在自然界中，现存的生物要么适应环境，要么被新物种取代。
Starting from different environmental resources, when reviewing the position of man in the relation of man and nature, they have also evaluated the value of nonhuman natural existent things.
他们从不同的环境资源为出发点，在反思人在人与自然关系中的地位同时，也评估了非人的自然存在物的价值。
This text introduces the chemistry of the environment pollution property of the heavy metals cadmium, such as existent appearance of nature.
介绍了重金属镉的环境污染化学性质，自然界存在的形态；
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