An iron wire is $8.0\ \text{m}$ long and has a diameter of $0.50\ \text{mm}$. Its resistance is $R$. Another iron wire is $2.0\ \text{m}$ long and has a diameter of $1.0\ \text{mm}$. What is the resistance of this second wire?
- A$\frac{R}{16}$
- B$\frac{R}{8}$
- C$\frac{R}{2}$
- D$R$