Question: who does meredith grey date after derek died
[{'answer': 'Nathan Riggs', 'provenance': [{'wikipedia_id': '7687013', 'title': 'Meredith Grey', 'start_paragraph_id': 31, 'start_character': 41, 'end_paragraph_id': 31, 'end_character': 53, 'bleu_score': 1.0, 'section': 'Section::::Storylines and Characteristics.\n'}]}, {'provenance': [{'wikipedia_id': '7687013', 'title': 'Meredith Grey', 'start_paragraph_id': 31, 'start_character': 0, 'end_paragraph_id': 31, 'end_character': 964, 'bleu_score': 0.9550947814056241, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 12039901734660836766}, 'section': 'Section::::Storylines and Characteristics.\n'}]}]