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