Billy Is in an Interrogation Room at a Police Station

Billy is in an interrogation room at a police station. He was brought there after being arrested on suspicion of DUI. He was not read his Miranda rights on the side of the road when he was taken into custody and was not read his Miranda rights upon arriving at the station either. The detective who enters the interrogation room is unaware of this information and begins questioning Billy about his whereabouts that evening. Billy mentions that he was at a bar called "The Floating Walrus." This piques the detectives interest, because a woman last seen at that bar has been reported missing. When the detective mentions her name, Billy breaks down crying and asks for forgiveness. Billy then says her body is in a wooded area about 250 feet behind the bar. The detective leaves the station, heads to that area, and finds the woman's body; she is dead from a gunshot wound. A gun registered to Billy is lying next to her.
-Let's now assume that Billy was in fact read Miranda warning before he was brought into the interrogation room. Let's also assume that, before he broke down and gave his confession, he had been through three grueling hours of interrogation, during which time he remained mostly silent. Which of the following is true?

A) The interrogation went on too long, and his statement about the body should be excluded.
B) Based on the Supreme Court's decision in Berghuis v. Thompkins, this statement will be admissible because Billy did not explicitly invoke his right to remain silent at any point.
C) Based on the Supreme Court's decision in Nix v. Williams, any evidence derived from this confession should be excluded.
D) The Miranda Rights were read for his DUI arrest and he should have been read a new set before being interrogated for murder.