Question: when was the i have a dream speech spoken
[{'answer': 'August 28 , 1963', 'provenance': [{'wikipedia_id': '18948383', 'title': 'I Have a Dream', 'start_paragraph_id': 1, 'start_character': 167, 'end_paragraph_id': 1, 'end_character': 183, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '18948383', 'title': 'I Have a Dream', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 447, 'bleu_score': 0.861651277313062, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7297516385273003943}, 'section': 'Section::::Abstract.'}]}]