Question: who is the leader of the t-birds in grease
[{'answer': 'Danny Zuko', 'provenance': [{'wikipedia_id': '336846', 'title': 'Grease (film)', 'start_paragraph_id': 1, 'start_character': 264, 'end_paragraph_id': 1, 'end_character': 274, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '336846', 'title': 'Grease (film)', 'start_paragraph_id': 15, 'start_character': 0, 'end_paragraph_id': 15, 'end_character': 131, 'bleu_score': 0.9181891462193901, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 2166681851788518923}, 'section': 'Section::::Cast.:Principal cast.\n'}]}]