Answer:
the correct one is the a, Â Â Â Uâ = 2 Uâ
Explanation:
The gravitational potential energy is
      U = m g h
if the stones reach the same height, the energy of the first stone is
      Uâ = mâ g h
The second stone is twice the mass and reaches the same height
       mâ = 2 mâ
potential energy is
      Uâ = mâ g h
      Uâ = 2 mâ g h
      Uâ = 2 Uâ
therefore the energy is double.
When reviewing the statements, the correct one is the a