As both the given triangles are congruent to each other the answer is A. ∠S.
The statement "ΔPQR ≅ ΔSTR" means that triangle PQR is congruent to triangle STR.
When two triangles are congruent, it means that their corresponding angles and sides are equal.
In this case, since ΔPQR ≅ ΔSTR, we can say that angle P is congruent to angle S.
So, the complete statement is: ∠P ≅ ∠S.