Question: when did ha long bay become a world heritage site
[{'answer': '1994', 'provenance': [{'wikipedia_id': '217913', 'title': 'Hạ Long Bay', 'start_paragraph_id': 4, 'start_character': 284, 'end_paragraph_id': 4, 'end_character': 288, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '217913', 'title': 'Hạ Long Bay', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 439, 'bleu_score': 0.9757530668325981, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4575336754427929062}, 'section': 'Section::::Abstract.'}]}]