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': 'Annealing of gold foil is the process by which \nSelect and explain. \nA. Contaminants are removed from the surface, B. Rigidity decreases and ductility increases, C. Both ductility and proportional limit decreases, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Because gold attracts gases that render it noncohesive, such gases must be removed from the surface of the gold before dental compaction. This process is usually referred to as degassing or annealing and is accomplished by application of heat. Degassing is the preferred term, because the desired result is to remove residual surface contamination (although further annealing, resulting in additional internal stress relief or recrystallization, may also occur in this process).', 'role': 'assistant'}]