Question: what kind of bombs were used in boston
[{'answer': 'Pressure cooker bombs', 'provenance': [{'wikipedia_id': '39131099', 'title': 'Pressure cooker bomb', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 21, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '39131099', 'title': 'Pressure cooker bomb', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 313, 'bleu_score': 0.9611463610973231, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 9877536442288982447}, 'section': 'Section::::Abstract.'}]}]