Final answer:
The HL (Hypotenuse-Leg) theorem supports the conclusion that the two triangles are congruent because they have a right angle and two corresponding sides equal (one hypotenuse and one leg each).
Step-by-step explanation:
The correct abbreviation of the postulate or theorem that supports the conclusion that the triangles are congruent, given that ∠c, ∠f are right angles; ac = df; and bc = ef, is HL (Hypotenuse-Leg) congruence theorem. This theorem states that in right triangles, if the hypotenuse and one leg of one triangle are equal to the hypotenuse and one leg of another triangle, then the triangles are congruent. Since both given triangles have a right angle and two corresponding sides (one hypotenuse and one leg) are congruent, they are indeed congruent by the HL congruence theorem.