$\begin{array}{*{20}{c}} {{{\rm{H}}_3}{\rm{C}} - {\rm{C}} = {\rm{CH}} - {\rm{C}} \equiv {\rm{C}} - {\rm{H}}}\\ {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}\\ {H\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \end{array}$માં સિગ્મા બંધની સંખ્યા $......$ છે.