Question: what is the biggest aircraft carrier in the us
[{'answer': 'Nimitz - class', 'provenance': [{'wikipedia_id': '181160', 'title': 'Nimitz-class aircraft carrier', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 21, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '181160', 'title': 'Nimitz-class aircraft carrier', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 422, 'bleu_score': 0.7359226767349251, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13623149107657481997}, 'section': 'Section::::Abstract.'}]}]