Answer:All balls have same velocity
Explanation:
Ball A
horizontal velocity
vertical velocity
let h be the height of building
Vertical velocity acquired by Ball A

Velocity just before hitting ground=
Ball B
launched with velocity u at angle of 45 above horizontal


horizontal velocity will remain same as there is no acceleration in that direction
vertical velocity just before hitting the floor


Final velocity before hitting ground 
Ball C


horizontal velocity will remain same as there is no acceleration in that direction
vertical velocity just before hitting the floor


Final velocity before hitting ground 
Thus all three balls will have same final velocity.