Answer:
![\boxed {\boxed {\sf Choice \ B }}](https://img.qammunity.org/2021/formulas/history/high-school/aw74vrtscpcejwsgpd5djjspax1477p7uj.png)
Step-by-step explanation:
The United States government contains federalism, which gives the federal government some powers and the state governments powers that both concur and differ.
The federal government is responsible for matters that affect the entire nation, so things like national defense, foreign affairs, and war.
The state governments have more localized responsibilities, such as public education, protect health and safety (sanitation is included), make marriage laws, and libraries.
So, the service the federal government provides is one that impacts the entire country. The best answer is B. National defense.