Question: when was purchase tax introduced in the uk
[{'answer': '1940', 'provenance': [{'wikipedia_id': '44815535', 'title': 'Purchase Tax', 'start_paragraph_id': 1, 'start_character': 38, 'end_paragraph_id': 1, 'end_character': 42, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]