Answer:
B. Thebes must punish the murderer of Laius.
Explanation:
In Oedipus the King, Part I, the instructions that Creon receives from the oracle is that Thebes must punish the murderer of Laius.
This was because the oracle was unhappy with the murderer of Laius and couldn't let him go unpunished so it charges Creon to bring the killer to justice.