Which of the following is not a criterion for congruence of triangles?

Prove that the medians of an equilateral triangle are equal.

$S$ is any point on side $QR$ of a $\triangle PQR$. Show that: $PQ + QR + RP > 2 \, PS$.

If in $\Delta ABC, AC > AB > BC$,then find the greatest angle of the triangle.

$ABCD$ is a quadrilateral such that diagonal $AC$ bisects the angles $A$ and $C.$ Prove that $AB = AD$ and $CB = CD.$

The image of an object placed at a point $A$ before a plane mirror $LM$ is seen at the point $B$ by an observer at $D$ as shown in the figure. Prove that the image is as far behind the mirror as the object is in front of the mirror.