In triangles $ABC$ and $PQR$,$\angle A = \angle Q$ and $\angle B = \angle R$. Which side of $\triangle PQR$ should be equal to side $AB$ of $\triangle ABC$ so that the two triangles are congruent? Give reason for your answer.

(N/A) In triangles $ABC$ and $PQR$,we have:
$\angle A = \angle Q$ (Given)
$\angle B = \angle R$ (Given)
For the two triangles to be congruent by the $ASA$ (Angle-Side-Angle) congruence rule,the side included between the two angles must be equal.
In $\triangle ABC$,the side included between $\angle A$ and $\angle B$ is $AB$.
In $\triangle PQR$,the side included between $\angle Q$ and $\angle R$ is $QR$.
Therefore,for the triangles to be congruent,side $AB$ must be equal to side $QR$ $(AB = QR)$.