Question: when did the first tanks appear in ww1
[{'answer': 'April 1917', 'provenance': [{'wikipedia_id': '2994067', 'title': 'Tanks in World War I', 'start_paragraph_id': 3, 'start_character': 40, 'end_paragraph_id': 3, 'end_character': 50, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '2994067', 'title': 'Tanks in World War I', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 124, 'bleu_score': 0.8151678595510181, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11275084166008211418}, 'section': 'Section::::Abstract.'}]}]