Answer:
BC congruent to EF
Step-by-step explanation:
Notice that you know that side AB in the first triangle is congruent to side DE in the second triangle, and that side AC in the forst triangle is congruent to side DF in the second one. Therefore, you need the third side on both triangles to be congruent, that way, the two whole triangles will be congruent.
Therefore, you need that:
BC congruent to EF
