Answer: C. Reflection
Explanation:
There are three rigid transformations which create congruent figures :
a)reflections, b) rotations, c) translations
A reflection is a transformation that flips a figure on the coordinate plane across a given line without changing the shape or size of the figure.
A translation moves a shapes by a particular distance.
A rotation rotates a shape around a fix point by an angle .
Therefore, the transformation can verify congruence by flipping a triangle over the y-axis is reflection.