Question: when did we go from imperial to metric
[{'answer': 'the mid -- 20th century'}, {'provenance': [{'wikipedia_id': '2732151', 'title': 'Metrication in the United Kingdom', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 764, 'bleu_score': 0.956047202777158, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5410644628638819219}, 'section': 'Section::::Abstract.'}]}]