Which of the following statements are correct?
(A) Centre of mass of a body always coincides with the centre of gravity of the body.
(B) Centre of mass of a body is the point at which the total gravitational torque on the body is zero
(C) A couple on a body produce both translational and rotational motion in a body.
(D) Mechanical advantage greater than one means that small effort can be used to lift a large load.