The answer that goes in the blank is

So

The order of the letters is important.
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Step-by-step explanation:
The sequence ABC has the letter A go first, B next, then C last. The order is important. This ordering will help us find the answer.
Note that the triangle ABC reflects over a horizontal line so that point A moves to F, point B moves to E, and point C moves to D.
This means that F is the first letter of the answer, E is the next, followed by D last. This means ABC in that exact order corresponds to FED in that exact order.
Therefore, triangle ABC is congruent to triangle FED
We write this as
