use the distance formula and Pythagorean theorem to proceed to the solution:
distance=√((x₂-x₁)²+(y₂-y₁)²), Pythagorean Theorem c²=a²+b²
a) (-5,6), (-5,-6), (4,-6)
d= √((-6-6)²+(-5+5)²)
d=12
d=√((-6+6)²+(4+5)²)= 9
d=√((-6-6)²+(4+5)²)= 15
A is correct