$A$ conducting metal circular wire loop of radius $r$ is placed perpendicular to a magnetic field which varies with time as $B = B_0 e^{-t/\tau}$,where $B_0$ and $\tau$ are constants. If the resistance of the loop is $R$,then the total heat generated in the loop after a long time $(t \to \infty)$ is:

• A
  $\frac{\pi^2 r^4 B_0^4}{2\tau R}$
• B
  $\frac{\pi^2 r^4 B_0^2}{2\tau R}$
• C
  $\frac{\pi^2 r^4 B_0^2 R}{\tau}$
• D
  $\frac{\pi^2 r^4 B_0^2}{\tau R}$