Answer:
The girl's feet are closer to the surface of the pool because

Explanation:
Girl's feet are
from the surface of a pool.
Boy's feet are
from the surface of a pool.
You may think that -0.75 is higher than -0.5, but that's false, because negative numbers work the opposite, the higher is the absolute value of a negative number, the lower is its value.
Therefore, the girl's feet are closer than the boy's, and the boy's feet are 0.25 feet away from the girl's feet.
So, the right answer is the first choice.