Final answer:
The correct option is A) Estonia.
Estonia is the country with the best quality of life in northeastern Europe, due to its successful integration into Western Europe, democratic governance, and high standards of living.
Step-by-step explanation:
When evaluating the quality of life in northeastern Europe, Estonia (A) stands out among the options provided. Estonia's transition from a Soviet republic to independence has been marked by its rapid integration into Western Europe, which includes joining the North Atlantic Treaty Organization (NATO) and the European Union (EU) in 2004.
The country has embraced market economies and democratic governments, which contribute to its high standards of living and prioritization of human rights, education, and social concerns. Conversely, the challenges faced by Moldova, Ukraine, and Belarus in terms of slow economic growth, authoritarian governance, and political instability suggest that these countries currently offer a lesser quality of life compared to Estonia.