A diverging lens of focal length f1 is placed in front of and coaxially with a concave mirror of focal length f2. Their separation is d. A parallel beam of light incident on the lens returns as a parallel beam from the arrangement.
(a) The beam diameters of the incident and reflected beams must be the same.
(b) d = 2|f2| - |f1|
(c) d = |f2| - |f1|
(d) If the entire arrangement is immersed in water, the conditions will remain unaltered.
