In vacuum all falling objects will have same acceleration.

The constant acceleration is due to gravitational force of earth and is known as acceleration due to gravity given by:

Where,

G = Gravitational Constant = Nm²kg^-2

M = Mass of Earth

R = Radius of Earth

From above, we see that all variables in the equation are constant. Thus g dosen’t depend on any other factors, and hence is constant.

Hence, option C is correct.