A spherical ball of mass `20kg` is stationary at the top of a hill of height `100m` , it rolls down a smooth surface to the ground , then climbs up another bill of height of `30 m` and final rolls down to a horizontal base at a height of `20 m` about the ground . The velocity attained by the ball is
A. `10 sqrt(30) m//s`
B. `10 m//s`
C. `20 m//s`
D. `40 m//s`