Economical problems are of inverse senses in adjacent level;

经济问题在相邻背景层次中意义逆反原理；

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However, some economical problems facing recycle of reclaimed water have restricted the wide use of it. These problems are analysed and some measures are offered in the paper.

但中水回用中面临的一些经济性方面的问题，制约了中水的广泛应用，文章对这些问题进行分析，并提出解决措施。

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Engineers apply the principles of science and mathematics to develop economical solutions to technical problems. Their work is the link between perceived social needs and commercial applications.

工程师利用科学和数学的基本原理发现最经济的方法来解决技术问题。他们的工作是联系潜在的社会需求和商业用途。

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