Question: what is the airport code for charlotte nc
[{'answer': 'CLT', 'provenance': [{'wikipedia_id': '264293', 'title': 'Charlotte Douglas International Airport', 'start_paragraph_id': 2, 'start_character': 254, 'end_paragraph_id': 2, 'end_character': 257, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]