Question: when did the chemical attack in syria happen 2017
[{'answer': '4 April', 'provenance': [{'wikipedia_id': '53684292', 'title': 'Khan Shaykhun chemical attack', 'start_paragraph_id': 1, 'start_character': 48, 'end_paragraph_id': 1, 'end_character': 55, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]