The correct answer is C) federal.
The power to establish post offices and post roads is held at the federal level.
This power is stated in the United States Constitution. You can read it on Article I, section 8, Clause 7. It is the Postal Clause that allows Congress to establish Post Roads and Post Offices to help communications between the states. This also allowed the government to charge some money to get revenue. This faculty is part of the enumerated powers of Congress.