How is a civil action commenced in federal court?

In the context of commencing a civil action in federal court, the correct choice is a complaint. A complaint is the formal legal document that initiates a lawsuit by outlining the plaintiff's claims against the defendant. It sets the stage for the legal process by detailing the grounds for the court's jurisdiction, the facts of the case, and the specific relief or damages being sought. Once the complaint is filed with the court, it allows the defendant to be properly notified and to respond to the allegations.

The other options do not serve as the primary means of beginning a civil action in federal court. A bill of information is typically used in criminal cases, not civil ones, to initiate charges against a defendant. A rule to show cause is usually employed to call upon a party to show reasons why a particular course of action should not be taken, which is not the same as commencing a lawsuit. A third-party demand refers to a procedural step in which a defendant brings another party into the lawsuit, but it cannot be used to initiate a civil action. Therefore, the complaint stands as the fundamental document that starts the process in federal civil litigation.