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 male 45 years old wants his missing teeth to be replaced. Intraoral examination reveals Kennedy class 4 edentulous  maxillary arch. Impression is made with hydrocolloid impression material.\nThe impression is placed in which of the following storage medium to prevent dimensional change? \nSelect and explain. \nA. 2% K2SO4 solution, B. 2% Na2SO4 solution, C. 2% NaNO3 solution, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Dimensional Stability\nOnce\xa0the\xa0hydrocolloid\xa0impression\xa0is\xa0removed\xa0from\xa0the mouth and exposed to air at room temperature, some shrinkage\xa0associated\xa0with\xa0syneresis\xa0and\xa0evaporation\xa0will\xa0occur. Conversely, if the impression is immersed in water, swelling caused\xa0by\xa0imbibition\xa0can\xa0occur. The storage medium, such as 2% potassium sulfate solution, or 100% relative humidity in a storage chamber, is suggested to reduce the dimensional change of agar impressions.\xa0\n100% relative humidity\xa0is\xa0the\xa0best\xa0storage\xa0environment\xa0to\xa0preserve\xa0the normal water content of the impression.', 'role': 'assistant'}]