Aprosecutor is a specific type of attorney who takes part in a criminal trial. what are his or her courtroom responsibilities?

to represent a defendant who cannot afford to hire an attorney for a trial.
to represent the litigants in the case and protect them from the reach of the government.
to represent the state or federal government in a prosecution of someone accused of a crime.
to represent the judge and work to ensure the proceedings of the trial are smooth.