Let \(f(x)\) be a continuous periodic function with period \(T\). Let \(I=\int_{a}^{a+T} f(x) d x\). Then
(A) I is linear function in 'a'
(B) I does not depend on 'a'
(C) \(0<\mathrm{I}<\mathrm{a}^{2}+1\) where \(\mathrm{I}\) depends on ' \(\mathrm{a}\) '
(D) \(\mathrm{I}\) is quadratic function in 'a'