Answer:
The two hypotenuses.
Explanation:
HL or Hypotenuse-Leg Theorem: two right triangles are congruent if and only if the hypotenuse and a leg of one right triangle are congruent to the hypotenuse and a leg of the other right triangle.
Since we already know the bottom leg of each triangle is congruent, we only need to know the two hypotenuses.