In the network shown, the potential difference between A and B is $\left(\mathrm{R}={\mathrm{r}}_1={\mathrm{r}}_2={\mathrm{r}}_3=1\mathrm{\Omega },{\mathrm{E}}_1=3\mathrm{V},{\mathrm{E}}_2=2\mathrm{V},{\mathrm{E}}_3=1\mathrm{V}\right)$

• A

  1 V

• B

  2 V

• C

  3 V

• D

  4 V