Final answer:
Answer is option a. Negotiating in an international forum is the most effective method to solve problems related to scarce or polluted resources that cross national boundaries, as it promotes cooperation and collective action, which are critical for environmental protection.
Step-by-step explanation:
To solve problems related to scarce or polluted resources that cross national boundaries, negotiating in an international forum is most likely to be effective. Unilateral actions may lead to tension and conflict, while importing or selling resources does not address the root problems of environmental protection or resource scarcity. International treaties, facilitated by organizations like the United Nations, help address the policy decisions of one state that can negatively affect the environment of another state. Such cooperation is essential since environmental issues do not respect political borders and often require collective action to be resolved effectively.
Concerns about multinational firms evading environmental laws or countries becoming too dependent on imported resources like oil also highlight the need for international cooperation. Without agreements, countries may fail to act on environmental protection, leading to a collective loss. Thus, creating and adhering to international agreements can provide the structure and incentives needed to manage shared resources sustainably and equitably.