Question: in the united kingdom who picks the prime minister
[{'answer': 'Monarch of the United Kingdom', 'provenance': [{'wikipedia_id': '24150', 'title': 'Prime Minister of the United Kingdom', 'start_paragraph_id': 1, 'start_character': 10, 'end_paragraph_id': 1, 'end_character': 40, 'bleu_score': 0.668740304976422, 'section': 'Section::::Abstract.'}]}]