In the following sequence of reactions, the alkene affords the compound '$$B$$' $$$CH_3 CH = CHCH_3 \xrightarrow{O_3} A \xrightarrow{H_2 O,\ Zn} B.$$$ The compound B is

A

$$CH_3 CH_2 CHO$$

B

$$CH_3 COCH_3$$

C

$$CH_3 CH_2 COCH_3$$

D

$$CH_3 CHO$$