In the following sequence of reactions, the alkene affords the compound ‘B’ $CH_3CH = CHCH_3 \xrightarrow{O_3} A \xrightarrow[\text{Zn}]{\text{$H_2O$}} B$ <br> The compound is :
( A ) $CH_3COCH_3$
( B ) $CH_3CH_2COCH_3$
( C ) $CH_3CHO$
( D ) $CH_3CH_2CHO$