In which reaction does the underlined compound act as a reducing agent?
- A$\text{CO}_2 + \text{C} \rightarrow 2\text{CO}$
- B$2\text{CuO} + \text{C} \rightarrow 2\text{Cu} + \text{CO}_2$
- C$\text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2$
- D$\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2$