Spectrum of a signal x(t), sampled at period T, is given by:

A

$$X_s(f) = \sum_{n = -\infty}^{\infty} X\left(f - \frac{n}{T}\right)$$

B

$$X_s(f) = \sum_{n = -\infty}^{\infty} X\left(nf - T\right)$$

C

$$X_s(f) = X\left(f - \frac{n}{T}\right)$$

D

$$X_s(f) = \sum_{n = -\infty}^{\infty} X\left(f - nT\right)$$