The answer is A. True.
This can be proven because of the HL Theorem. This theorem states that any two right triangles (triangles that both have right angles) that have one leg congruent and their hypotenuses (the "leg" across from the right angle) congruent, that these two triangles are congruent.
In the diagram, ABC and DEF must be congruent, because they are both right triangles, and share congruent hypotenuses and legs (HL Theorem).
