Question: when was the first tank used in ww1
[{'answer': '15 September 1916', 'provenance': [{'wikipedia_id': '2994067', 'title': 'Tanks in World War I', 'start_paragraph_id': 27, 'start_character': 150, 'end_paragraph_id': 27, 'end_character': 167, 'bleu_score': 1.0, 'section': 'Section::::First Deployments.\n'}]}, {'provenance': [{'wikipedia_id': '2994067', 'title': 'Tanks in World War I', 'start_paragraph_id': 27, 'start_character': 0, 'end_paragraph_id': 27, 'end_character': 1205, 'bleu_score': 0.9908464411502881, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11471087284445617235}, 'section': 'Section::::First Deployments.\n'}]}]