In which equation does carbon undergo both oxidation and reduction?
- A$\text{C} + \text{O}_2 \rightarrow \text{CO}_2$
- B$\text{CO}_2 + \text{C} \rightarrow 2\text{CO}$
- C$3\text{CO} + \text{Fe}_2\text{O}_3 \rightarrow 3\text{CO}_2 + 2\text{Fe}$
- D$2\text{CO} + \text{O}_2 \rightarrow 2\text{CO}_2$