a
\(\begin{array}{*{20}{c}}
  {Ph - C{H_2} - CH - C{H_3}\xrightarrow{{B{r_2}/hv}}} \\ 
  {|\,\,\,\,\,\,\,\,\,\,} \\ 
  {D\,\,\,\,\,\,\,\,\,\,} 
\end{array}\)

\(\begin{array}{*{20}{c}}
  {Ph - \mathop {{\text{ }}C}\limits^* H - \mathop {{\text{ }}C}\limits^* H - C{H_3}} \\ 
  {|{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} \,\,\,\,\,\,\,\,\,\,\,\,{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} |{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} \,\,\,\,{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} } \\ 
  {Br{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} \,\,\,\,\,\,{\mkern 1mu} {\mkern 1mu} \,\,\,\,{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} D\,\,\,\,{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} } 
\end{array}\)