If (1 + x)n = C0 + C1x + C2x2 +..........+ Cnxn, then the sum of the products of the Ci’s taken two at a time represented by \(\sum \sum C_iC_j (0\le i<j\le n)\) is equal to
(a) 22n–1
(b) \(2^n - \frac{(2n)!}{2(n!)^2}\)
(c) \(2^{2n-1} - \frac{(2n)!}{2(n!)^2}\)
(d) None of these