A is the answer.
Congruent has the meaning of being exactly the same.
The sides of the 2 triangles are proportional, where each side of the triangle on the left can be multiplied by the same number (I.e. 5) to give you each side of the triangle on the right:
8 × 5 = 40
6 × 5 = 30
10 × 5 = 50
Since the corresponding sides of triangles are proportional, it means that their corresponding angles are exactly the same (I.e. congruent). *** This applies to any other triangles with the same proportions.
Hope this helps! :)