Three identicle particle each of mass `1 kg` are placed with their centres on a straight line. Their centres are marked `A, B and C` respectively. The distance of centre of mass of the system from `A` is.
A. `(PQ + PR +QR)/(3)`
B. `(PQ + PR)/3`
C. `(PQ + QR)/3`
D. None of the above