Early Chemists (Well, Neolithic Metals Workers Actually!) Discovered That Carbon

Early chemists (well, Neolithic metals workers actually!) discovered that carbon, such as coal or charcoal, could be used to convert metal salts into metals. What was the role of the carbon in this process?

A) To react with oxygen in the air.
B) To oxidize the metals.
C) To burn away the oxygen in the metal salts.
D) To act as a reducing agent.
E) None of the above.