instruction:
Given a factoid/trivia type question, generate the topic of the question. The topic is the entity the question talks about.
question:
The Battle of Antietam was fought during which war?
answer:
battle of antietam

question:
In which book of the Bible are the Ten Commandments first mentioned?
answer:
bible

question:
In Greek myth, who was the son of Agamemnon and Clytemnestra, who killed his mother to avenge his father's death?
answer:
agamemnon