The focal length of a spherical mirror and a thin spherical lens is − 20 𝑐𝑚. The mirror and the lens are likely to be

Here, the mirror and lens are both concave. In the given case, a spherical mirror and a thin spherical lens both have a − 20 𝑐𝑚 focal length. The focal length for both mirror and lens is negative, then both mirror and lens are concave. As we know, the lens and mirror of a convex of positive focal length, and the lens and mirror of a concave for negative focal length. 

Hence option (a) both concaves, is correct