求翻译：CBA是一种有用的工具，可以分析政府投资项目的净收益和社会回报。在实践中，与其说成本—效益分析是一门科学倒不如说是一种。为了计算项目产品的收益，必须做出许多简化后的假设。此外，当项目涉及外部负效应时，专家们对如何评价外部负效率通常存在巨大分歧是什么意思？

CBA is a useful tool that can analyze net return on government investment and social projects.

CBA is a useful tool, can analyze the net income and society of government investment project repays. In practice, cost - benefit analysis is a science rather is an art. For the income of computational item product, must come up with hypotheses after many simplifications. In addition, exterior when

CBA is one kind of useful tool, may analyze the government investment plan the net income and the society repays.In reality, if said the cost - benefit analysis is a science would rather said is one kind of art.In order to calculate the project product the income, after must make many simplification

CBA is a useful tool, you can analyze the Government's net income and return on social investment projects. In practice, the cost-benefit analysis is not so much a science as it is an art form. In order to calculate the product of the project proceeds, after many simplifying assumptions must be made

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