Question: where does the river mekong start and end
[{'answer': 'Lasagongma Spring'}, {'answer': 'Mekong Delta', 'provenance': [{'wikipedia_id': '69147', 'title': 'Mekong', 'start_paragraph_id': 26, 'start_character': 213, 'end_paragraph_id': 26, 'end_character': 225, 'bleu_score': 1.0, 'section': 'Section::::Course.\n'}]}]