SSS congruence is side-side-side congruence, which is a method to prove triangles congruent by all three sides of the triangle being congruent. The other choices all involve congruent angles. Therefore, the bottom left choice is the best answer.
Also, notice that the bottom left choice shows which side is congruent to which. All three sides of one of the triangles are shown to be congruent with the corresponding side to the other triangle, therefore, congruent by SSS.
