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Answer: (A) 75°
Explanation
According to the SAS (Side-Angle-Side) congruence criterion, two triangles are congruent if two sides and the included angle of one triangle are equal to the corresponding two sides and the included angle of the other triangle.
In triangle ABC, the given sides are AC = 2.5 cm and BC = 5 cm, and the included angle between these two sides is ∠C = 75°.
In triangle DEF, the given sides are DE = 2.5 cm and DF = 5 cm. The included angle between these two sides is ∠D.
For the triangles to be congruent, their corresponding sides and the included angles must be equal. Under the correspondence where AC matches DE and BC matches DF, the included angle ∠C must match the included angle ∠D. Therefore, ∠D must equal ∠C, which gives ∠D = 75°.