Question: where does carbon fixation occur in c4 plants
[{'answer': 'in the mesophyll cells', 'provenance': [{'wikipedia_id': '492012', 'title': 'C4 carbon fixation', 'start_paragraph_id': 5, 'start_character': 200, 'end_paragraph_id': 5, 'end_character': 222, 'bleu_score': 1.0, 'section': 'Section::::pathway.\n'}]}]