In the following sequence of reactions,the alkene affords the compound 'B':$CH_3CH=CHCH_3\quad\underrightarrow {O_3}\quad A\quad\underrightarrow {H_2O}\quad B$.The compound B is

Question

$\begin{array}{1 1}(a)\;CH_3CHO&(b)\;CH_3CH_2CHO\\(c)\;CH_3COCH_3&(d)\;CH_3CH_2COCH_3\end{array}$