$A$ concave mirror of focal length $f_{1}$ is placed at a distance $d$ from a convex lens of focal length $f_{2}$. $A$ parallel beam of light coming from infinity parallel to the principal axis falls on the convex lens and then after refraction falls on the concave mirror. If the light is to retrace its path,the distance $d$ should be:

• A
  $f_{1} + f_{2}$
• B
  $-f_{1} + f_{2}$
• C
  $2f_{1} + f_{2}$
• D
  $2f_{1} - f_{2}$