Question: when did the us give up control of the panama canal
[{'answer': 'December 31 , 1999'}, {'provenance': [{'wikipedia_id': '315787', 'title': 'Panama Canal Zone', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 679, 'bleu_score': 0.7972668934795131, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16286834708717046333}, 'section': 'Section::::Abstract.'}]}]