From the top of a tower of height h, a body is projected horizontally with velocity U on reaching the ground, the magnitude of change in velocity 
 

• A

  $\sqrt{{\mathrm{U}}^2+2\mathrm{gh}}$

• B

  $\sqrt{2\mathrm{gh}}$

• C

  $\mathrm{U}-\sqrt{2\mathrm{gh}}$

• D

  $\mathrm{U}+\sqrt{2\mathrm{gh}}$