The basic principle of cost behaviour is that as the level of activity rises, costs will usually rise.

成本行为的基本特征是：作业水平上升，则成本通常也上升。

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Such behaviour carries a cost: while the city's debt is rising, its steep streets are increasingly pot-holed, its parks unwatered, its street-lighting patchier.

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One is higher taxes, to make polluters pay the full cost of their anti-social behaviour.

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Offering insurance at a fixed, low cost will also have an unintended effect on behaviour: the sickest people will be the first to buy, since they expect the highest medical costs in the future.

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