Question: when did environmental pollution began to emerge as a problem in the united states
[{'answer': 'the 1960s', 'provenance': [{'wikipedia_id': '10183', 'title': 'Environmental movement in the United States', 'start_paragraph_id': 53, 'start_character': 221, 'end_paragraph_id': 53, 'end_character': 230, 'bleu_score': 1.0, 'section': 'Section::::History.:"Post-environmentalism".\n'}]}]