Which equation represents the reduction of copper?
- A$\text{CuO} + \text{C} \rightarrow \text{Cu} + \text{CO}$
- B$2\text{CuS} + 3\text{O}_2 \rightarrow 2\text{CuO} + 2\text{SO}_2$
- C$\text{Cu}(g) \rightarrow \text{Cu}(l)$
- D$\text{Cu}(l) \rightarrow \text{Cu}(s)$