Which of the following is a congruence transformation? a. reflecting b. stretching c. dilating

a. reflecting

Step-by-step explanation:

The rigid transformations are the transformation which transform any figure to exactly congruent image because it preserves the side length and the angles of a figure.

Reflection is a rigid transformation that  flips a figure to create a new figure. It is called so because it always produces the image which is the same size and shape as the pre-image .

Hence, reflection is a congruence transformation.

Stretching and dilation both changes the size of the actual figure therfore they do not produce congruent images.