Question: when did starcraft 2 go free to play
[{'answer': 'April 19 , 2017', 'provenance': [{'wikipedia_id': '14271726', 'title': 'StarCraft', 'start_paragraph_id': 4, 'start_character': 179, 'end_paragraph_id': 4, 'end_character': 194, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '14271726', 'title': 'StarCraft', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 290, 'bleu_score': 0.8902056737869241, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 8099989918365553255}, 'section': 'Section::::Abstract.'}]}]