Question: when did angel leave buffy the vampire slayer
[{'answer': '1999', 'provenance': [{'wikipedia_id': '693254', 'title': 'Angel (Buffy the Vampire Slayer)', 'start_paragraph_id': 6, 'start_character': 1753, 'end_paragraph_id': 6, 'end_character': 1757, 'bleu_score': 1.0, 'section': 'Section::::Appearances.:"Buffy the Vampire Slayer".\n'}]}, {'provenance': [{'wikipedia_id': '693254', 'title': 'Angel (Buffy the Vampire Slayer)', 'start_paragraph_id': 8, 'start_character': 0, 'end_paragraph_id': 8, 'end_character': 1357, 'bleu_score': 0.975786456511559, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1133016523341638461}, 'section': 'Section::::Appearances.:"Angel".\n'}]}]