Answer: DF
Explanation:
We know that if two triangles are congruent then the corresponding sides are congruent ( CPCTC ).
Given :

Then, corresponding sides of
and
are congruent.
i.e. AB must be congruent to FH [First two letters]
BC must be congruent to HD [Last two letters]
CA must be congruent to DF [last and first letter]
∴ Side correspond to side CA = DF
Hence, the correct answer is "DF"