Question: who has the lowest era in mlb history
[{'answer': 'Tim Keefe', 'provenance': [{'wikipedia_id': '10348914', 'title': 'List of Major League Baseball annual ERA leaders', 'start_paragraph_id': 5, 'start_character': 61, 'end_paragraph_id': 5, 'end_character': 70, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '10348914', 'title': 'List of Major League Baseball annual ERA leaders', 'start_paragraph_id': 5, 'start_character': 0, 'end_paragraph_id': 5, 'end_character': 1210, 'bleu_score': 0.9576778125999981, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3111337334353460156}, 'section': 'Section::::Abstract.'}]}]