Select correct statements of the following :
a) Algebraic sum of moments of masses about centre of mass is zero
b) For small bodies, centre of mass coincides with centre of gravity
c) Position of centre of mass of a body depends on co-ordinate system
d) Position of centre of mass is independent of mass distribution

According to principle of moments, moments about COM of the system as a whole always add up to zero. 

A small body's centre of mass and centre of gravity are always congruent. A body's centre of gravity is where all of its gravitational torque is zero. A couple on a body causes the body to move in both directions, translation and rotation.

Position of centre of mass does not depend on co-ordinate system but depends on the mass distribution of the body.

Hence the correct answer is a & b are correct.