Using a pencil, a line with length $30\ \text{cm}$ and width $1.2\ \text{mm}$ is made. The resistivity of the pencil material is $2.0 \times 10^{-5}\ \Omega\,\text{m}$, and the resistance of the line is $40\ \text{k}\Omega$. What is the thickness of the line?
- A$1.25 \times 10^{-10}\ \text{m}$
- B$1.25 \times 10^{-8}\ \text{m}$
- C$1.25 \times 10^{-7}\ \text{m}$
- D$1.25 \times 10^{-5}\ \text{m}$