Answer:
a. Macbeth
Step-by-step explanation:
Macbeth is the one who utters this words after "discovering" that Duncan has bene murdered. In this quote, we learn that Macbeth acts shocked to hear of this death. He tells us that everything good in the world is over now because of the death. However, the reader knows that Duncan's death is in fact a consequence of Macbeth's actions.