A square pulse of $3$ volts amplitude is applied to $C-R$ circuit shown in the figure. The capacitor is initially uncharged. The output voltage $\mathrm{V}_{0}$ at time $t=2 \mathrm{sec}$ is
- $3 \mathrm{~V}$
- $-3 \mathrm{~V}$
- $4 \mathrm{~V}$
- $-4 \mathrm{~V}$