To prove that these two triangles are congruent by Hypotenuse Leg theorem, we need to know that a hypotenuse and a leg are congruent or equal. Since we already see that a leg is congruent, we now need to know that the hypotenuses are congruent. The hypotenuses are CA and DA, meaning that to prove that these two triangles are congruent by HL, we need to know that CA is congruent to DA, or the second option.
