Question

what is kept inside abcd ​

Answer 1

It is a model of torch so, that the light rays are diver ging due to convex mirror

Answer 2

A concave lens may be kept inside ABCD.

Light rays passing through a concave lens diverge from each other, as shown in the fig. They appear to deviate away from the principal focus of the lens. $\quad$

If there was convex lens inside ABCD then the light rays would converge each other and they appear to pass through the principal focus of the lens.