Question: what geographic feature separates north africa from the rest of africa
[{'answer': 'desert', 'provenance': [{'wikipedia_id': '1854', 'title': 'Geography of Africa', 'start_paragraph_id': 19, 'start_character': 83, 'end_paragraph_id': 19, 'end_character': 89, 'bleu_score': 1.0, 'section': 'Section::::Plains.\n'}]}, {'provenance': [{'wikipedia_id': '1854', 'title': 'Geography of Africa', 'start_paragraph_id': 19, 'start_character': 0, 'end_paragraph_id': 19, 'end_character': 439, 'bleu_score': 0.9751504244977051, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17276982980166062093}, 'section': 'Section::::Plains.\n'}]}]