The correct answer is Miranda v. Arizona, as that Supreme Court's decision lets American citizens know they have the right to remain silent and the right to an attorney.
Miranda against Arizona was a decision of the Supreme Court of the United States. The court held that both incriminating and exculpatory statements made in response to an interrogation by a defendant in police custody are admissible in a trial only if the prosecution can show that the defendant was informed before being questioned of what is currently known as Miranda warning: his right to consult a defense lawyer before and during interrogation, and the right not to self-incriminate himself. And besides, the defendant should not only understand these rights, but he should also give them up voluntarily.