Question: what year did cadillac stop using the northstar engine
[{'answer': '2011', 'provenance': [{'wikipedia_id': '859304', 'title': 'Northstar engine series', 'start_paragraph_id': 1, 'start_character': 111, 'end_paragraph_id': 1, 'end_character': 115, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '859304', 'title': 'Northstar engine series', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 358, 'bleu_score': 0.7495784851520301, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7537230575264020370}, 'section': 'Section::::Abstract.'}]}]