I'm too late to win, but I guess I'll provide an explanation to why the answer is A from just my brain(I'm bad at physics, don't quote me on anything.
B isn't right because kinetic energy is (mass * velocity²)/2 and velocity increases as it falls down.
C isn't right because as its falling, its getting faster.
D isn't right because velocity is just speed with a direction so it can't remain constant.
That leaves, A, and earth gravity is 9.81 m/s² and its always constant(or around there).
How wrong was I?