Question: when was the last episode of er aired
[{'answer': 'April 2 , 2009', 'provenance': [{'wikipedia_id': '22262196', 'title': 'And in the End...', 'start_paragraph_id': 1, 'start_character': 121, 'end_paragraph_id': 1, 'end_character': 138, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '22262196', 'title': 'And in the End...', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 187, 'bleu_score': 0.9419661180380051, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16209935355198197137}, 'section': 'Section::::Abstract.'}]}]