Question: in what year was the source code for the linux kernel released
[{'answer': '1991', 'provenance': [{'wikipedia_id': '21347315', 'title': 'Linux kernel', 'start_paragraph_id': 3, 'start_character': 46, 'end_paragraph_id': 3, 'end_character': 50, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]