Final answer:
Terrifying dreams haunt Macbeth and Lady Macbeth as a result of their guilty conscience following their role in King Duncan's murder.
Step-by-step explanation:
Macbeth and Lady Macbeth often experience terrifying dreams in Macbeth due to b) They have a guilty conscience. After conspiring and executing the murder of King Duncan, both characters struggle with the weight of their actions. Macbeth hears voices saying, 'Macbeth does murder sleep', which indicates his awareness of his guilt disrupting his rest. Lady Macbeth tries to steel herself and Macbeth for their deeds but eventually succumbs to guilt and madness, leading to sleepwalking and hallucinations. These dreams and disturbances are direct consequences of their choices and the psychological burden they carry.