When you have a triangle with a 90 degree angle and a hypotenuse of 10, the other can´t be determined without another angle, or another side, the same for the little triangle with just the hypotenuse you can not calculate the size of the other sides or the other angles, and just by sight you can not make a correct statement about the similarity of the triangles.
I'm not sure for my answer 'cuz I just learned this but i think its A because even though the size changes, the corresponding angle measure are the same and the corresponding sides are proportional.
