Evaluate

${\displaystyle \int \frac{dx}{e^x – 1}}$

(Note: C is a constant of integration)

1. $\frac{e^x}{e^x -1}$ + C
2. $\frac {In(e^x -1)}{e^x}$ + C
3. In$(\frac {e^x}{e^x -1})$ + C
4. In(1 – e$^{-x}$) + C