Fill in the following blanks with suitable words:

(a) Parallel rays of light are reflected by a ______ to a point called the principal focus.

(b) The focal length of a concave mirror is the distance from the principal focus to the ____.

(c) A______ converges rays of light whereas a ______ diverges rays of light.

(d) For a convex mirror, parallel rays of light appear to ___ from a point called the principal focus