$A$ circular loop made of thin copper wire of mass $m$ is placed in a uniform magnetic field such that the plane of the loop is perpendicular to the magnetic field. If $d$ and $\rho$ are the density and resistivity of copper respectively and the magnetic field varies at a constant rate of $\frac{dB}{dt}$,then the induced current in the loop is . . . . . .

• A
  $\frac{4 \pi m}{\rho d}\left(\frac{dB}{dt}\right)$
• B
  $\frac{m}{4 \pi \rho d}\left(\frac{dB}{dt}\right)$
• C
  $\frac{\pi m}{4 \rho d}\left(\frac{dB}{dt}\right)$
• D
  $\frac{4 m}{\pi \rho d}\left(\frac{dB}{dt}\right)$