C) He agreed to work for Dumbledore as the new Divination teacher.
Explanation:
After Dolores Umbridge dismissed Sybill Trelawney, Dumbledore hired him to teach Divination instead of her.
Other centaurs considered this a dishonorable act and expelled it from the herd.
In The Half-Blood Prince, Trelawney taught divination again, but because of Flrenze's herd problem, Dumbledore decided that both should teach divination at the same time until Firenze's return to the Forest after the Battle of Hogwarts.
