Which of the following statements are correct ?

Question

$\begin{array}{1 1} \text{(a) Centre of mass of a body always coincides with the center of gravity of the body.}\\ \text{(b)Center of mass of a body is the point at which the total gravitational torque on the body is zero.} \\ \text{(c)A couple on a body produce both translational and rotational motion in a body} \\\text{(d)Mechanical advantage greater than one means that small effort can be used to lift a large load.} \end{array}$