He Sixth Amendment protects the rights of all citizens. People suspected of crimes. People on trial in criminal court. People in prison.

The answer is C - people who are on trial in criminal court.

The Sixth Amendment states that: In all criminal prosecutions, the accused shall enjoy the right to a speedy and public trial, by an impartial jury of the State and district wherein the crime shall have been committed, which district shall have been previously ascertained by law, and to be informed of the nature and cause of the accusation; to be confronted with the witnesses against him; to have compulsory process for obtaining witnesses in his favor, and to have the Assistance of Counsel for his defence.

So, the correct answer is: People on trial in criminal court. The Sixth Amendment protects all people on trial in the United States, including non-citizens. It is the original rules of the game for criminal trials.