Question: when did delhi became an important commercial centre
[{'answer': '12th century', 'provenance': [{'wikipedia_id': '4953782', 'title': 'History of Delhi', 'start_paragraph_id': 1, 'start_character': 309, 'end_paragraph_id': 1, 'end_character': 321, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '4953782', 'title': 'History of Delhi', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 879, 'bleu_score': 0.7724723052635971, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 12735972373481411008}, 'section': 'Section::::Abstract.'}]}]