Question: when did the us policy of containment begin
[{'answer': '1946', 'provenance': [{'wikipedia_id': '425279', 'title': 'Containment', 'start_paragraph_id': 3, 'start_character': 47, 'end_paragraph_id': 3, 'end_character': 51, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '425279', 'title': 'Containment', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 336, 'bleu_score': 0.629494300063136, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3563813274419982154}, 'section': 'Section::::Abstract.'}]}]