A balloon from rest accelerates uniformly upward with 'a' ms^-2. A stone is released from the balloon. Now, read the following statements to pick the right ones.
a) The stone's initial velocity is zero, relative to balloon
b) The stone's initial velocity is nonzero, relative to earth
c) The time taken to reach the ground from the balloon's frame of reference is inversely proportional to $\sqrt{(\mathrm{a}+\mathrm{g})}$.
d) The time take to reach the ground from earth's frame of reference is directly proportional to $\sqrt{(\mathrm{a}+\mathrm{g})}$.