Question: what is the back up sight used in sar 21 in the event of optical scope failure
[{'answer': 'iron sights', 'provenance': [{'wikipedia_id': '1013301', 'title': 'SAR 21', 'start_paragraph_id': 18, 'start_character': 12, 'end_paragraph_id': 18, 'end_character': 23, 'bleu_score': 1.0, 'section': 'Section::::Design issues.\n'}]}]