Question: when was the like button introduced on facebook
[{'answer': 'February 9 , 2009', 'provenance': [{'wikipedia_id': '45394372', 'title': 'Facebook like button', 'start_paragraph_id': 4, 'start_character': 221, 'end_paragraph_id': 4, 'end_character': 238, 'bleu_score': 1.0, 'section': 'Section::::Use on Facebook.\n'}]}, {'provenance': [{'wikipedia_id': '45394372', 'title': 'Facebook like button', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 970, 'bleu_score': 0.956218543751134, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1993400967349668509}, 'section': 'Section::::Abstract.'}]}]