Question: the southern border of the sahara desert is known as the
[{'answer': 'the Sahel', 'provenance': [{'wikipedia_id': '325363', 'title': 'Sahara', 'start_paragraph_id': 2, 'start_character': 392, 'end_paragraph_id': 2, 'end_character': 401, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '325363', 'title': 'Sahara', 'start_paragraph_id': 10, 'start_character': 0, 'end_paragraph_id': 10, 'end_character': 564, 'bleu_score': 0.9212315174844051, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 2925056828374413521}, 'section': 'Section::::Geography.\n'}]}]