Question: who is the headmaster of hogwarts after dumbledore died
[{'answer': 'Severus Snape', 'provenance': [{'wikipedia_id': '947583', 'title': 'Hogwarts staff', 'start_paragraph_id': 12, 'start_character': 368, 'end_paragraph_id': 12, 'end_character': 381, 'bleu_score': 1.0, 'section': 'Section::::Notable teachers and staff members.:Filius Flitwick.\n'}]}]