Answer: D. Dante believed betrayal is the worst sin because of the pain it causes others.
Treachery, or betrayal, was considered by Dante to be the worst sin of all. Therefore, those who commited it during their lifetime were placed in the ninth circle of Hell. This was the last circle, and the one where Lucifer was imprisoned.
Some historical and mythological characters that are imprisoned here are Nimrod (created the Tower of Babel), Ephialtes (tried to storm Mount Olympus), Cassius and Brutus (who betrayed Julius Caesar) and Judas Iscariot (who betrayed Jesus Christ).