Question: when did microwaves become a common household appliance
[{'answer': '1967', 'provenance': [{'wikipedia_id': '58017', 'title': 'Microwave oven', 'start_paragraph_id': 2, 'start_character': 681, 'end_paragraph_id': 2, 'end_character': 685, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '58017', 'title': 'Microwave oven', 'start_paragraph_id': 2, 'start_character': 40, 'end_paragraph_id': 2, 'end_character': 926, 'bleu_score': 0.772906974894024, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16161775133487874684}, 'section': 'Section::::Abstract.'}]}]