A concave lens never forms a real image of a real object. Which of the following is the chief reason?
a) Because the focal length of a concave lens is negative, the lens formula makes v positive for any real object.
b) Because the rays refracted by a concave lens always diverge and can only appear to meet when produced backward.
c) Because the principal focus of a concave lens lies on the same side as the object, so a real image would have to form inside the lens which is impossible.
d) Because the optical power of a concave lens is smaller than that of a convex lens of the same magnitude of focal length, and therefore it cannot bring light to an actual focus.