Question: when did the united states declare a war on cancer by passing the national cancer act
[{'answer': '1971', 'provenance': [{'wikipedia_id': '14088001', 'title': 'War on Cancer', 'start_paragraph_id': 1, 'start_character': 333, 'end_paragraph_id': 1, 'end_character': 337, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '14088001', 'title': 'War on Cancer', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 496, 'bleu_score': 0.9375874466695201, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14707601158514662983}, 'section': 'Section::::Abstract.'}]}]