How can you obtain benzene from acetylene?

Identify $\mathrm{A}, \mathrm{B}$ and $\mathrm{C}$. Explain the reaction:

${\mathrm{CaC}}_2\stackrel{{\mathrm{H}}_2\mathrm{O}}{\to }\mathrm{A}\underset{{\mathrm{HgSO}}_4}{\overset{\mathrm{dil}. {\mathrm{H}}_2{\mathrm{SO}}_4}{\to }}\mathrm{B}\stackrel{\mathrm{Ni}/{\mathrm{H}}_2}{\to }\mathrm{C}$