Question: machine which converts ac into dc is known as
[{'answer': 'rectifier', 'provenance': [{'wikipedia_id': '60569', 'title': 'Rectifier', 'start_paragraph_id': 1, 'start_character': 2, 'end_paragraph_id': 1, 'end_character': 11, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '60569', 'title': 'Rectifier', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 603, 'bleu_score': 0.7599725480293631, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1504438801426202212}, 'section': 'Section::::Abstract.'}]}]