Professor Pretty and his colleagues calculated the externalities of British agriculture for one particular year.
普雷蒂教授和他的同事计算了某一年英国农业的外部性。
2
The fact that burning fuel creates these "negative externalities" does not imply that no tax on fuel could ever be too high.
燃烧燃料产生这些“负外部性”的事实并不意味着燃油税不会太高。
3
Economics is precise about the tax that should, in principle, be levied to deal with negative externalities: the tax on a liter of fuel should be equal to the harm caused by using a liter of fuel.