Question: which is the busiest airport in the uk
[{'answer': 'London - Heathrow', 'provenance': [{'wikipedia_id': '13836704', 'title': 'List of busiest airports in the United Kingdom', 'start_paragraph_id': 2, 'start_character': 97, 'end_paragraph_id': 2, 'end_character': 113, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '13836704', 'title': 'List of busiest airports in the United Kingdom', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 657, 'bleu_score': 0.9563334828258161, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11756562428236023580}, 'section': 'Section::::Abstract.'}]}]