A unitary system of government is characterized by a central authority that holds the majority of the power, with any sub-national entities (like states or provinces) deriving their authority from the central government. Given this definition, none of the provided statements explicitly describe a unitary system.
However, the closest option could be:
States can establish rules that cities have to follow
This option implies a hierarchy where a central authority (the states) can dictate rules to lower levels of government (cities), though in a strict unitary system, the central government would typically make such rules directly.
If you are looking for the most relevant option that aligns with the characteristics of a unitary system, that would be the one.