The question has asked us to determine how we know the two triangles in the figure given are congruent.
From the image, MO has the same length as AD.
Also, we can notice that side OP on the first image is the same as length AB in the second triangle.
And finally, we can see that MP is the same as BD
From this, we can see that both triangles are congruent, because all three sides on one triangle is the same as the other triangle.
Therefore, final answer is SSS (Option A)