Question: when did the exxon valdez oil spill happen
[{'answer': 'March 24 , 1989', 'provenance': [{'wikipedia_id': '10243', 'title': 'Exxon Valdez oil spill', 'start_paragraph_id': 1, 'start_character': 71, 'end_paragraph_id': 1, 'end_character': 86, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '10243', 'title': 'Exxon Valdez oil spill', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 912, 'bleu_score': 0.7932821941097221, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1776970243601055978}, 'section': 'Section::::Abstract.'}]}]