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
Duplex steel is made up of: 
Select and explain. 
A. Martensitic steel and austenitic steel, B. Ferritic grain of stainless steel, C. Ferritic + austenitic grains of stainless steel, D. Ferritic + martensitic grains of stainless steel
C: Ferritic + austenitic grains of stainless steel
Answer: C: Ferritic + austenitic grains of stainless steel 
Explanation: Duplex stainless steel is a combination of both ferritic and austenitic grains of stainless steel. The basic chemical composition of duplex stainless steel is an equal mix of ferrite and austenite. This combination creates some very beneficial properties for this family of stainless steels.