A copper wire measuring $80\,\text{cm}$ in length and having a cross-sectional area of $0.20\,\text{mm}^2$ is found to have resistance $R$. For a copper wire with cross-sectional area $0.40\,\text{mm}^2$, what length gives resistance $R$?
- A10 cm
- B20 cm
- C40 cm
- D160 cm