Statement (a) is incorrect because the centre of mass coincides with the centre of gravity only in a uniform gravitational field. If the gravitational field varies across the body, they may not coincide . Statement (b) is correct. The centre of gravity is defined as the point about which the total gravitational torque on the body is zero . Statement (c) is incorrect. A couple consists of two equal and opposite forces whose lines of action do not coincide. The net force is zero, so it produces pure rotational motion without any translational motion . Statement (d) is correct. Mechanical Advantage (M.A.) is defined as the ratio of load to effort (M.A. = Load / Effort). If M.A. > 1, then Effort < Load, meaning a small effort can lift a large load . Thus, statements (b) and (d) are correct.