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': 'Disadvantage of polysulphide as impression material: \nSelect and explain. \nA. High cost, B. Materials leaching out, C. Stretching leads to distortion, D. Difficulty in cast pouring', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]