Question: when was the clock tower in london built
[{'answer': '1859', 'provenance': [{'wikipedia_id': '7290308', 'title': 'Big Ben', 'start_paragraph_id': 2, 'start_character': 82, 'end_paragraph_id': 2, 'end_character': 86, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '7290308', 'title': 'Big Ben', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 423, 'bleu_score': 0.6185649791055791, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3478231212162998376}, 'section': 'Section::::Abstract.'}]}]