To which court system do city courts belong?
a. the state court system
b. the local court system
c. the federal court system
d. the municipal court system

City courts belong to the state court system. Option A is correct.

City court is a court of law with jurisdiction limited to a city or other municipality. It generally deals with "violations of city ordinances and may also have jurisdiction over minor criminal cases, as well as over certain civil cases."

State courts constitute courts of "general jurisdiction". They hear all the cases not specifically selected for federal courts. Federal courts interpret federal laws, while state courts interpret state laws.