Question: when was the last time the us had a trade surplus
[{'answer': '1975', 'provenance': [{'wikipedia_id': '28946427', 'title': 'United States balance of trade', 'start_paragraph_id': 11, 'start_character': 35, 'end_paragraph_id': 11, 'end_character': 39, 'bleu_score': 1.0, 'section': 'Section::::Impacts.\n'}]}, {'provenance': [{'wikipedia_id': '28946427', 'title': 'United States balance of trade', 'start_paragraph_id': 11, 'start_character': 0, 'end_paragraph_id': 11, 'end_character': 115, 'bleu_score': 0.9021315316859231, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 18306032554057079297}, 'section': 'Section::::Impacts.\n'}]}]