Question: when did led zeppelin write stairway to heaven
[{'answer': 'in late 1971', 'provenance': [{'wikipedia_id': '255999', 'title': 'Stairway to Heaven', 'start_paragraph_id': 1, 'start_character': 79, 'end_paragraph_id': 1, 'end_character': 91, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '255999', 'title': 'Stairway to Heaven', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 306, 'bleu_score': 0.9645876452711911, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14111392159095445587}, 'section': 'Section::::Abstract.'}]}]