Final answer:
a. Supreme Court.
The Supreme Court has original jurisdiction when a state sues another state, as mandated by the United States Constitution. It is the only federal court with both original and appellate jurisdiction, and the specific authority to hear cases involving states as parties falls under its original jurisdiction.
Step-by-step explanation:
If a state sued another state, the correct answer would be a. Supreme Court. According to Article III of the United States Constitution, the Supreme Court has both original and appellate jurisdiction. However, it specifies that the Supreme Court has original jurisdiction only in cases in which a state is a party, as well as cases affecting ambassadors, public ministers, and consuls. Thus, when one state sues another state, it is the Supreme Court that has the authority to hear the case first, before any other court.
It's important to note that while the Supreme Court has original jurisdiction in some cases, most cases come to it on appeal. This dual capability makes the Supreme Court unique in the federal court system, as it is the only court to have both types of jurisdiction.
Federal district courts, on the other hand, are generally the trial-level courts with original jurisdiction over federal cases, and appellate courts, including Circuit Courts of Appeal, handle appeals. State courts deal with state matters. For matters involving federal law, or when jurisdiction is concurrent, the federal and state courts can sometimes both have jurisdiction. However, when a state is a party in a lawsuit, the Supreme Court is the designated court to hear such a case first.