$A$ block of mass $m$ is sliding down an inclined plane with constant speed. At a certain instant $t_0$,its height above the ground is $h$. The coefficient of kinetic friction between the block and the plane is $\mu$. If the block reaches the ground at a later instant $t_g$,then the energy dissipated by friction in the time interval $(t_g - t_0)$ is

• A
  $\mu m g h$
• B
  $\mu m g h / \sin \theta$
• C
  $m g h$
• D
  $\mu m g h / \cos \theta$