Which of the following statements are true about the acceleration due to gravity of the Earth (where $r$ is the distance from the center of the Earth and $R$ is the radius of the Earth)?
$(a)$ $g$ decreases when moving away from the center, if $r > R$.
$(b)$ $g$ decreases when moving away from the center, if $r < R$.
$(c)$ $g$ is zero at the center of the Earth.
$(d)$ $g$ at the equator decreases, if the Earth stops rotating about its axis.

• A
  $(a) \& \ (b)$
• B
  $(a), (b) \& \ (c)$
• C
  $(a) \& \ (c)$
• D
  $(a), (b), (c) \& \ (d)$