Final answer:
The correct answer to the question is D) taxes. Subsidies, patents, copyrights, and vouchers are all tools that can help achieve an efficient allocation of resources in the presence of external benefits, while taxes are not typically used for external benefits but more for mitigating negative externalities.
Step-by-step explanation:
The question pertains to the various devices the government can use to achieve a more efficient allocation of resources when there are external benefits. To clarify the options provided:
- Subsidies like vouchers can be used by the government to increase consumption of beneficial goods or services.
- Patents and copyrights protect intellectual property and provide an incentive for innovation and R&D.
- Taxes can be employed to reduce negative externalities and reallocate resources efficiently, but they are not typically used to address external benefits.
- Vouchers, specifically, act as a form of subsidy to encourage the consumption of goods with positive externalities.
Therefore, the correct answer to the question -- which device is an exception when trying to increase the efficiency in the presence of external benefits -- is D) taxes, as the other options are supportive measures.