Question: which of the following is the designation for bedrock a. o b. a c. r d. c
[{'answer': 'R', 'provenance': [{'wikipedia_id': '1522331', 'title': 'Soil horizon', 'start_paragraph_id': 3, 'start_character': 252, 'end_paragraph_id': 3, 'end_character': 253, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]