Question: what is the tallest monument in the united states
[{'answer': 'Gateway Arch', 'provenance': [{'wikipedia_id': '53353', 'title': 'Gateway Arch', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 12, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '53353', 'title': 'Gateway Arch', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 612, 'bleu_score': 0.7373359333127311, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10054828878040262854}, 'section': 'Section::::Abstract.'}]}]