Let α, β and γ be three positive real numbers. Let f(x) = αx5 + βx3 + γx, x ∈ R and g : R → R be such that g(f(x)) = x for all x ∈ R. If a1 , a2 , a3, .....an be in arithmetic progression with mean zero, then the value of \(f(g(\frac{1}{n}\displaystyle\sum_{i=1}^{n}f(a_ i)))\) is equal to :
(A) 0
(B) 3
(C) 9
(D) 27