a
\(\begin{array}{*{20}{c}}
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,O} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,||} \\
{C{H_3}C{H_2}MgBr + Ph - C - C{H_3}\xrightarrow{{(2){H^ + }}}}
\end{array}\begin{array}{*{20}{c}}
{\,\,\,\,\,\,OH} \\
{|\,\,} \\
{Ph - C - C{H_3}} \\
{|\,\,\,} \\
{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,C{H_2} - C{H_3}}
\end{array}\)