Question: when was the brundtland definition of sustainability written
[{'answer': '1987', 'provenance': [{'wikipedia_id': '579149', 'title': 'Brundtland Commission', 'start_paragraph_id': 1, 'start_character': 793, 'end_paragraph_id': 1, 'end_character': 797, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '579149', 'title': 'Brundtland Commission', 'start_paragraph_id': 7, 'start_character': 0, 'end_paragraph_id': 7, 'end_character': 633, 'bleu_score': 0.978138775770484, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7920959619162929792}, 'section': 'Section::::History.\n'}]}]