There are 3 set of parallel lines containing p lines, q lines and r lines resp. The greatest no. of parallelograms that can be formed by the system _______
(a) pqr + (p-1) (q-1) (r-1)
(b) 1/4 { pqr + (p-1) (q-1) (r-1)}
(c) 1/4 pqr (p+1) (q+1) (r+1)
(d) None of these