The Fourier series representation of an impules train denoted by
\[s(t)=\sum_{n=-\infty}^{n} d\left(t-n \mathrm{~T}_{0}\right) \text { is given by }\]
- $\frac{1}{\mathrm{~T}_{0}} \sum_{n=-\infty}^{\infty} \exp -\frac{j 2 \pi n t}{\mathrm{~T}_{0}}$
- $\frac{1}{\mathrm{~T}_{0}} \sum_{n=-\infty}^{\infty} \exp -\frac{j \pi n t}{\mathrm{~T}_{0}}$
- $\frac{1}{\mathrm{~T}_{0}} \sum_{n=-\infty}^{\infty} \exp \frac{j \pi n t}{\mathrm{~T}_{0}}$
- $\frac{1}{\mathrm{~T}_{0}} \sum_{u=-\infty}^{\infty} \exp \frac{j 2 \pi n t}{\mathrm{~T}_{0}}$