Final answer:
Researchers produce the efficient quantity of research and development when compensated for the marginal social benefits. Patents and copyrights cannot always ensure efficient R&D due to potential monopolistic conditions. The correct answer is A) social; social; cannot.
Step-by-step explanation:
The question discusses the relationship between research and development (R&D) practices in a market economy and the economic concept of externalities. Specifically, the question addresses how research and development can lead to social benefits and externalities, and how the market may provide insufficient incentives for their optimal provision.
When researchers receive a voucher equal to the marginal social benefit, they are incentivized to produce the efficient quantity of R&D, as this aligns their personal incentives with the broader social good. If researchers receive a subsidy equal to the marginal external benefit, they are compensated for the positive spillovers their work creates that benefit others, encouraging more investment in R&D.
As for patents and copyrights, while they provide incentives for innovation by allowing creators to capture some of the benefits of their work, they may not always result in an efficient amount of research and development. This is because they can also create monopolistic conditions that may lead to higher prices and restricted access to new technologies. Thus, the statement that patents and copyrights cannot result in an efficient amount of research and development aligns with the possible inefficiencies they introduce.
The correct answer to the student's question is: A) social; social; cannot.