The closer you are to the ground the more accurate you'll be. That's why most snipers are in the "prone" position.
B. It's an example of velocity due to the fact that it has a measurement of speed, divided by time, and has a specific direction. Acceleration doesn't have any direction on it, but has speed divided by time. C and D have a different mode of measurement despite of the fact that it still needs meters/miles/km.
To solve this problem we will apply the concepts related to the work theorem for which it is defined as the product of Force and distance. In turn, we will use the energy conservation theorem for which the applied work must be equivalent to the total kinetic energy on the body.
The work is defined as

Here,
F = Force
d = Displacement
Replacing with our values we have that


Now by conservation of energy,



Solving for v,


Therefore the correct answer is D.