Question: what is the tallest building in san fransisco
[{'answer': 'Salesforce Tower', 'provenance': [{'wikipedia_id': '10788731', 'title': 'List of tallest buildings in San Francisco', 'start_paragraph_id': 1, 'start_character': 133, 'end_paragraph_id': 1, 'end_character': 149, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]