Answer:
A) Reflection.
Explanation:
From the figure shown, we can see that the blue triangle is flipped about the x-axis to form the red triangle.
When an object is flipped about a line, then this transformation is called reflection about that line.
Thus, we can say that reflection is taking place in the figure shown in which the x-axis is acting like a mirror. The blue triangle is the pre-image and the red triangle is the image after reflection.
The reflection about x-axis is given by:
We can check the co-ordinates of the triangles and confirm the the transformation occurring
Points of pre-image triangle:

Points of image triangle

Thus, the transformation is reflection.