b
\(\mathop {\begin{array}{*{20}{c}} {\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_3}} \\ {\,\,\,\,\,\,\,\,\,\,\,\,\,|} \\ {C{H_3}C{H_2} - CH - CH - C{H_2}C{H_3}} \\ {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\ {\,\,\,\,\,\,C{H_2}\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\ {|\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \\ {\,\,\,\,\,\,\,C{H_3}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,} \end{array}}\limits_{3 - ethyl - 4 - methyl\,hexane} \)