Question: when is the litany of the saints sung
[{'answer': 'at the Easter Vigil', 'provenance': [{'wikipedia_id': '1701092', 'title': 'Litany of the Saints', 'start_paragraph_id': 18, 'start_character': 41, 'end_paragraph_id': 18, 'end_character': 60, 'bleu_score': 1.0, 'section': 'Section::::Catholic practice.:At the Easter Vigil.\n'}]}, {'provenance': [{'wikipedia_id': '1701092', 'title': 'Litany of the Saints', 'start_paragraph_id': 18, 'start_character': 0, 'end_paragraph_id': 18, 'end_character': 649, 'bleu_score': 0.9828310228624961, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17734872119656599288}, 'section': 'Section::::Catholic practice.:At the Easter Vigil.\n'}]}]