A man runs towards a mirror at a speed 15 m/s.  The speed of the image relative to the man is  

• A

  $15{\mathrm{ms}}^{-1}$

• B

  $30{\mathrm{ms}}^{-1}$

• C

  $35{\mathrm{ms}}^{-1}$

• D

  $20{\mathrm{ms}}^{-1}$