The correct answer is the letter C
Here a brief summary, on the part of the book that explains what happened:
Macbeth writes to his wife, Lady Macbeth, about prophecies he received from witches. When Duncan, the king of Scotland, decides to stay at Macbeth's castle in Inverness, Lady Macbeth throws a plan to assassinate him and conquer the throne for her husband. Although Macbeth is concerned about regicide, his wife finally persuades him, questioning his human condition, to follow his plan. On the night of the king's visit, Lady Macbeth intoxicates the guards so that Macbeth can enter the king's quarters and kill Duncan.
The murder leaves Macbeth so shaken that Lady Macbeth has to take control of the situation, picking up the bloody dagger from her husband's hands. According to her plan, she incriminates Duncan's servants, asleep because of the drunkenness of the night before, by the murder, putting daggers of blood among them.
