Answer:
C. not similar, dilations are involved
Explanation:
For geometric figures, such as triangles, we generally study a couple of kinds of transformations.
One is the "rigid transformation" which lets us move, rotate, or reflect the figure any way we like, but we keep it the same size—as though it were cut from cardboard or anything else that holds its shape and size. Any figures transformed by a rigid transformation are congruent.
Another is very much like the "rigid transformation", but dilation is involved. That is, the figure is allowed to be stretched or shrunk uniformly (by the same factor in every direction). Figures transformed in this way are similar, but are not congruent.
In this diagram, your triangle has been reflected and changed in size by a different factor horizontally than vertically. Hence dilation is involved (answer choices A or C), but because the factors are different, the figures are not similar (answer choice C).
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Comment on the answer choices
Rotations may be involved in similarity transformations, too. For some reason, that possibility was left off of choices A and C. (On the other hand, rotation is equivalent to a suitable set of reflections.)