This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'A problem with a porcelain jacket is it: \nSelect and explain. \nA. Is not color stable, B. Is very brittle, C. Has a very high compression strength, D. Is irritating to the gingiva', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]