The simpliest way is to use the AAS Postulate.
AAS Postulate: If two angles and the non-included side of one triangle are equal to the corresponding angles and side of another triangle, the triangles are congruent.
From the diagram you have:
1. one pair of angles with measure 40°;
2. one pair of angles with measure 60°;
3. the non-included side of one triangle is congruent to the non-included side of another triangle (their lengths are 10).
Answer: correct choice is D (AAS)
