Question: why leaves of cactus are reduced to spines
[{'answer': 'defending against herbivores', 'provenance': [{'wikipedia_id': '7819', 'title': 'Cactus', 'start_paragraph_id': 1, 'start_character': 954, 'end_paragraph_id': 1, 'end_character': 982, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'providing some shade', 'provenance': [{'wikipedia_id': '7819', 'title': 'Cactus', 'start_paragraph_id': 1, 'start_character': 1060, 'end_paragraph_id': 1, 'end_character': 1080, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'help prevent water loss by reducing air flow close to the cactus'}, {'provenance': [{'wikipedia_id': '7819', 'title': 'Cactus', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 1333, 'bleu_score': 0.9681469111527521, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15465749674468677218}, 'section': 'Section::::Abstract.'}]}]