Question: when did the british hand-over sovereignty of hong kong back to china
[{'answer': '1 July 1997', 'provenance': [{'wikipedia_id': '2093431', 'title': 'Handover of Hong Kong', 'start_paragraph_id': 1, 'start_character': 187, 'end_paragraph_id': 1, 'end_character': 198, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]