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': 'Casting flux is used to \nSelect and explain. \nA. Prevent the oxidation of material during melting., B. Increase the melting point of the flux., C. Prevent the contamination of the metal and theliner., D. All of the above.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Fluxes are specifically used\n\nTo remove gas or prevent its absorption into the melt.\nTo reduce metal loss.\nTo remove specific impurities and nonmetallic inclusions\nTo refine metallic constituents, or to lubricate and control surface structure in the semi-continuous casting of metal\xa0alloys.\n\nKey concept\nFlux powder may be sprinkled\xa0over the molten metal to reduce the oxides and increase fluidity for casting.', 'role': 'assistant'}]