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
Pickling: 
Select and explain. 
A. Is accomplished by soaking the casting in baking soda, B. Causes porosity in gold, C. Removes surface oxides from gold castings, D. Remove investment from gold casting
C: Removes surface oxides from gold castings
Answer: C: Removes surface oxides from gold castings 
Explanation: None