A cylindrical drum is pushed along by a board of length l. The drum rolls forward on the ground a distance of $\frac{\mathrm{l}}{2}$ . There is no slipping at any instant. During the process of pushing the board, the distance moved by the man on the ground is:

• A

  $\frac{\mathrm{l}}{2}$

• B

  $\frac{3\mathrm{l}}{4}$

• C

  I

• D

  none of these