Question: when did the construction of the world trade center begin
[{'answer': 'August 1968', 'provenance': [{'wikipedia_id': '7777427', 'title': 'Construction of the World Trade Center', 'start_paragraph_id': 4, 'start_character': 62, 'end_paragraph_id': 4, 'end_character': 73, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '7777427', 'title': 'Construction of the World Trade Center', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 502, 'bleu_score': 0.977139080690077, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14681396577790749095}, 'section': 'Section::::Abstract.'}]}]