$CH _{3} CH _{2} CH = CH _{2}$ $\xrightarrow[{Rh\,\,catalyst}]{{{H_2}/CO}}$
$[A]\,\,\begin{array}{*{20}{c}} {C{H_3} - C - {O^ - }} \\ {\,\,||} \\ {\,\,O} \end{array}$
$[B]\,\,CH_3O^-$
$[C]\,\,CN^-$
$[D]\,\,$