Question: where is the mouth of the river severn and what is it called
[{'answer': 'Severn Estuary', 'provenance': [{'wikipedia_id': '50807', 'title': 'River Severn', 'start_paragraph_id': 2, 'start_character': 46, 'end_paragraph_id': 2, 'end_character': 60, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'Bristol Channel , United Kingdom'}]