d
Let potential at point $\mathrm{E}$ be $\mathrm{V}$ and $\mathrm{A}, \mathrm{B}, \mathrm{C}$ are neutral point. (zero potential point)
Apply $\mathrm{KCL}$ at point $\mathrm{E}$
$\frac{\mathrm{V}-10}{1}+\frac{\mathrm{V}-30}{2}+\frac{\mathrm{V}+50}{2}=0$
$2(v-10)+V-30+V+50=0$
$4 \mathrm{V}=0 \quad \Rightarrow \quad \mathrm{V}=0$