Choose the correct alternative :
(a) Acceleration due to gravity increases/decreases with increasing altitude.
(b) Acceleration due to gravity increases/decreases with increasing depth (assume the earth to be a sphere of uniform density).
(c) Acceleration due to gravity is independent of mass of the earth/mass of the body.
(d) The formula −GMm(1/r2−1/r1) is more/less accurate than the formula mg(r2−r1) for the difference of potential energy between two points r2 and r1 distance away from the center of the earth.