Question: who plays derek's sister nancy on grey's anatomy
[{'answer': 'Davidtz', 'provenance': [{'wikipedia_id': '705774', 'title': 'Embeth Davidtz', 'start_paragraph_id': 0, 'start_character': 7, 'end_paragraph_id': 0, 'end_character': 14, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '705774', 'title': 'Embeth Davidtz', 'start_paragraph_id': 12, 'start_character': 0, 'end_paragraph_id': 12, 'end_character': 454, 'bleu_score': 0.9757530668325981, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 6208096996854848566}, 'section': 'Section::::Hollywood career.\n'}]}]