Hey!
It will be reduction because you're comparing the larger triangle to the smaller triangle.
Let's use the height as an example. The height of the larger triangle is 9. The height of the smaller triangle is 3. When reducing, the answer will be less than 1. Therefore, it will be 1/3 because 3 is 1/3 of 9
That means your answer is d.
Good luck and hope this helps!