Question: who played rebecca's mother on this is us
[{'answer': 'Elizabeth Perkins', 'provenance': [{'wikipedia_id': '52995471', 'title': 'List of This Is Us characters', 'start_paragraph_id': 113, 'start_character': 12, 'end_paragraph_id': 113, 'end_character': 29, 'bleu_score': 1.0, 'section': 'Section::::Guest stars.:Introduced in season one.\n'}]}]