The best way for a county to implement foreign policy is?

Multilaterally.

Explanation: Multilaterally is fundamental to politics and the economy.

The concept can be perceived as a form of cooperation, especially with regard to international diplomacy and actions that allow countries to respect limits.

These boundaries that countries face are at social, economic, political and national and international security levels.

Multilaterally is the result of an important historical process that can be observed over the decades. Once states realized that they could not alone solve issues that could harm other nations.

the answer to fill in the blank in this question would be the word resource, it is defined as the money, material or people (since human resource is a very valuable good) that a company or a person has at disposition (meaning they can use the resource as they see fit), to be able to complete a task or achieve a goal.  

letter a is the answer