A spherical ball of mass $20\text{ kg}$ is stationary at the top of a hill of height $100\text{ m}$. It rolls down a smooth surface to the ground, then climbs up another hill of height $30\text{ m}$ and finally rolls down to a horizontal base at a height of $20\text{ m}$ above the ground. The velocity attained by the ball is:

1. A
   $40\text{ m/s}$
2. B
   $20\text{ m/s}$
3. C
   $10\text{ m/s}$
4. D
   $10\sqrt{30}\text{ m/s}$