Which statement proves that △XYZ is an isosceles right triangle?

Which statement proves that △XYZ is an isosceles right triangle?

a. XZ ⊥ XY
b. XZ = XY = 5
c. The slope of XZ is , the slope of XY is , and XZ = XY = 5.
d. The slope of XZ is , the slope of XY is , and the slope of ZY = 7.