Question: what kind of bomb did the us drop on japan
[{'answer': 'nuclear weapons', 'provenance': [{'wikipedia_id': '11778948', 'title': 'Atomic bombings of Hiroshima and Nagasaki', 'start_paragraph_id': 1, 'start_character': 32, 'end_paragraph_id': 1, 'end_character': 47, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]