Final answer:
The lowest level of the federal court system is the district court, where federal cases are first tried. Losing parties can appeal to the circuit courts, and the Supreme Court is the final level of appeal.
Step-by-step explanation:
The lowest level of the federal court system is c. district court. The federal court system in the United States operates on a three-tiered structure. Initially, federal cases are tried in the district courts where evidence is presented, and witnesses testify. District courts are trial courts at the federal level. If a party is dissatisfied with the decision of a district court, they have the option to appeal to the circuit courts, also known as the U.S. courts of appeals, where decisions of the lower courts are reviewed without holding trials. The circuit courts are considered intermediate appellate courts. The final level of appeal in the federal system is the U.S. Supreme Court, which may choose to hear cases from the circuit courts or state supreme courts, particularly when there is a significant federal question involved.