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
Cleaning of base metal alloy is done by: 
Select and explain. 
A. Warm HCl, B. Cold HF, C. Cold H2SO4, D. Sandblasting with aluminium oxide
D: Sandblasting with aluminium oxide
Answer: D: Sandblasting with aluminium oxide 
Explanation: SANDBLASTING
Sandblasting is the process by which particles of an abrasive (usually aluminum oxide) is projected at high velocity using compressed air in a continuous stream. The casting is held in a sandblasting machine to clean the remaining investment from the surface of alloy.