Question: when did the us dollar become reserve currency
[{'answer': 'After World War II', 'provenance': [{'wikipedia_id': '177666', 'title': 'Reserve currency', 'start_paragraph_id': 7, 'start_character': 0, 'end_paragraph_id': 7, 'end_character': 18, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'provenance': [{'wikipedia_id': '177666', 'title': 'Reserve currency', 'start_paragraph_id': 7, 'start_character': 0, 'end_paragraph_id': 7, 'end_character': 339, 'bleu_score': 0.9645876452711911, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3731480425882626031}, 'section': 'Section::::History.\n'}]}]