# The below reaction involves

$\begin{array}{1 1}(a)\;\text{nucleophilic addition across double bond}\\(b)\;\text{free radical addition across double bond}\\(c)\;\text{electrophilic addition across double bond}\\(d)\;\text{no effect of the CO group on the C=C bond}\end{array}$

Above reaction is only nucleophilic addition across double bond is belived to take place by the following mechanism.
Hence (a) is the correct answer.