An iron rod is placed parallel to magnetic field of intensity $2000 \mathrm{~A} / \mathrm{m}$. The magnetic flux through the rod is $6 \times 10^{-4} \mathrm{~Wb}$ and its cross-sectional area is $3 \mathrm{~cm}^{2}$. The magnetic permeability of the rod in $\mathrm{Wb} / \mathrm{A}-\mathrm{m}$ isA) $10^{-1}$B) $10^{-2}$C) $10^{-3}$D) $10^{-4}$