Which of the following is an example of a power reserved to the states?

The correct choice, education policy, exemplifies a power reserved to the states because education is primarily governed at the state level. Each state has the authority to create its own educational systems, establish school curricula, determine funding mechanisms, and set regulations. This decentralization of education allows states to tailor their policies to meet the specific needs of their populations and communities, reflecting the principles outlined in the Tenth Amendment of the U.S. Constitution, which reserves powers not specifically granted to the federal government for the states.

In contrast, the other options represent powers that are typically reserved for the federal government. Declaring war and engaging in foreign diplomacy are powers explicitly granted to the federal government in the Constitution, as they relate to national security and international relations. Similarly, establishing a national currency falls under federal jurisdiction, as it involves the regulation of money supply and economic policy, further emphasizing the clear distinction between state and federal powers.