Question: who is the lead singer of doobie brothers
[{'answer': 'Tom Johnston', 'provenance': [{'wikipedia_id': '172878', 'title': 'The Doobie Brothers', 'start_paragraph_id': 2, 'start_character': 103, 'end_paragraph_id': 2, 'end_character': 115, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'Michael McDonald', 'provenance': [{'wikipedia_id': '172878', 'title': 'The Doobie Brothers', 'start_paragraph_id': 2, 'start_character': 246, 'end_paragraph_id': 2, 'end_character': 262, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '172878', 'title': 'The Doobie Brothers', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 614, 'bleu_score': 0.808403320361458, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11204340224489978377}, 'section': 'Section::::Abstract.'}]}]