For this case we have that by definition, the Pythagorean theorem states that:

Where:
c: It is the hypotenuse of the triangle
a, b: They are the legs of the triangle
Then, we verify if the theorem for the given triangles is fulfilled:
Triangle 1:

It is fulfilled!
Triangle 2:

It is not fulfilled!
Triangle 3:

It is not fulfilled!
ANswer:
Triangle A