Answer:
B.
Explanation:
If the given right triangles are similar, that meanst they have a ration in common, that is, one of them can be double size the other one. In other words, they are related by a scale ratio.
Notice, that one hypothenuse is double the other one, that is, 10 is double than 5. Also, 8 is double than 4. This means the scale factor is 2, one triangle has double size than the other.
Therefore, the proportion that relates these triangles is

or

Therefore, the right answer is B.