Question: who was sent to the rio grande to claim the southern border of texas
[{'answer': 'John Slidell', 'provenance': [{'wikipedia_id': '27143322', 'title': 'History of Texas (1845–1860)', 'start_paragraph_id': 6, 'start_character': 372, 'end_paragraph_id': 6, 'end_character': 384, 'bleu_score': 1.0, 'section': 'Section::::Mexican–American War.\n'}]}, {'provenance': [{'wikipedia_id': '27143322', 'title': 'History of Texas (1845–1860)', 'start_paragraph_id': 6, 'start_character': 0, 'end_paragraph_id': 6, 'end_character': 740, 'bleu_score': 0.943689856108147, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7940559643944154119}, 'section': 'Section::::Mexican–American War.\n'}]}]