A block of mass M is placed on a rough horizontal surface. A force F = M g acts on the block. It is inclined to the vertical at an angle $\mathrm{\theta }$. The coefficient of friction is µ. The block can be pushed along the surface only when

• A

  $\tan \mathrm{\theta }\ge \mathrm{\mu }$

• B

  $\cot \mathrm{\theta }\ge \mathrm{\mu }$

• C

  $\tan \mathrm{\theta }/2\ge \mathrm{\mu }$

• D

  $\cot \mathrm{\theta }/2\ge \mathrm{\mu }$