The AAS congruence theorem uses two adjacent angles, followed by a side length on the side (not in between the angles.) Therefore, the first answer is ruled out (because it deals with angles and not sides), and the second answer is ruled out because it involves side lengths between angles. LP=MO may be true, but it does not compare the two triangles that we are interested in. However, the last answer choice is correct, because a midpoint divides a line exactly in half, meaning that both halves are the same length and therefore congruent. Therefore, the last answer choice is correct. Hope this helps!
which becomes 
and you get
