A concave mirror of focal length $'f_1'$ is placeed at a distance of 'd' from a convex lens of focal length $'f_2'$ A beam of light coming from infinity and falling on this convex lens- concave mirror combination returns to infinity. The dsitance 'd' must equal

Question

( A ) $–2f_1 + f_2$
( B ) $–f_1 + f_2$
( C ) $f_1 + f_2$
( D ) $2f_1 + f_2$