Which of the following can make a parallel beam of light when light from a point source is incident on it?

(A) Concave mirror as well as convex lens
Try to understand simply, when a point source of light is placed at the focus of concave mirror then all light rays after reflection through mirror will become parallel to the principal axis. On the other hand, when this point source of light is placed at the focus of convex lens then after refraction by light rays convex lens will become parallel to the principal axis. Hence, your answer will be option [A].