The correct answer to the question "Which is an example of a public service?" is the fire department.
1. Public services are services provided by the government to the general public for the benefit of society as a whole.
2. The fire department is a classic example of a public service as it is funded and operated by the government to respond to emergencies, such as fires, accidents, and other incidents that require specialized assistance.
3. Unlike private schools, grocery stores, and gas stations which are typically operated by private businesses for profit, the fire department exists to serve the community and ensure public safety.
In summary, the fire department stands out as an example of a public service due to its essential role in protecting lives and property in the community.